feat: Define ServiceLoadBalancer Configuration API (#778)

**What problem does this PR solve?**:
This adds an optional configuration for the ServiceLoadBalancer Addon,
consisting of one or more IPv4 address ranges, e.g.,

```yaml
apiVersion: cluster.x-k8s.io/v1beta1
kind: Cluster
metadata:
  name: <NAME>
spec:
  topology:
    variables:
      - name: clusterConfig
        value:
          addons:
            serviceLoadBalancer:
              provider: MetalLB
              configuration:
                addressRanges:
                - start: 10.100.1.1
                  end: 10.100.1.20
                - start: 10.100.1.51
                  end: 10.100.1.70
```

(This is a copy of
#763.
I had to close that after
#755
added required checks that can't be run from PRs from public forks. )

**Which issue(s) this PR fixes**:
Fixes #

**How Has This Been Tested?**:
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api/v1alpha1/addon_types.go

@@ -257,4 +257,25 @@ type ServiceLoadBalancer struct {
 	// +kubebuilder:validation:Enum=MetalLB
 	// +kubebuilder:validation:Required
 	Provider string `json:"provider"`
+
+	// Configuration for the chosen ServiceLoadBalancer provider.
+	// +kubebuilder:validation:Optional
+	Configuration *ServiceLoadBalancerConfiguration `json:"configuration,omitempty"`
+}
+
+type ServiceLoadBalancerConfiguration struct {
+	// AddressRanges is a list of IPv4 address ranges the
+	// provider uses to choose an address for a load balancer.
+	// +kubebuilder:validation:Required
+	// +kubebuilder:validation:MinItems=1
+	AddressRanges []AddressRange `json:"addressRanges"`
+}
+
+// AddressRange defines an IPv4 range.
+type AddressRange struct {
+	// +kubebuilder:validation:Format=ipv4
+	Start string `json:"start"`
+
+	// +kubebuilder:validation:Format=ipv4
+	End string `json:"end"`
 }

api/v1alpha1/crds/caren.nutanix.com_awsclusterconfigs.yaml

@@ -218,6 +218,31 @@ spec:
                       type: object
                     serviceLoadBalancer:
                       properties:
+                        configuration:
+                          description: Configuration for the chosen ServiceLoadBalancer provider.
+                          properties:
+                            addressRanges:
+                              description: |-
+                                AddressRanges is a list of IPv4 address ranges the
+                                provider uses to choose an address for a load balancer.
+                              items:
+                                description: AddressRange defines an IPv4 range.
+                                properties:
+                                  end:
+                                    format: ipv4
+                                    type: string
+                                  start:
+                                    format: ipv4
+                                    type: string
+                                required:
+                                  - end
+                                  - start
+                                type: object
+                              minItems: 1
+                              type: array
+                          required:
+                            - addressRanges
+                          type: object
                         provider:
                           description: |-
                             The LoadBalancer-type Service provider to deploy. Not required in infrastructures where

api/v1alpha1/crds/caren.nutanix.com_dockerclusterconfigs.yaml

@@ -218,6 +218,31 @@ spec:
                       type: object
                     serviceLoadBalancer:
                       properties:
+                        configuration:
+                          description: Configuration for the chosen ServiceLoadBalancer provider.
+                          properties:
+                            addressRanges:
+                              description: |-
+                                AddressRanges is a list of IPv4 address ranges the
+                                provider uses to choose an address for a load balancer.
+                              items:
+                                description: AddressRange defines an IPv4 range.
+                                properties:
+                                  end:
+                                    format: ipv4
+                                    type: string
+                                  start:
+                                    format: ipv4
+                                    type: string
+                                required:
+                                  - end
+                                  - start
+                                type: object
+                              minItems: 1
+                              type: array
+                          required:
+                            - addressRanges
+                          type: object
                         provider:
                           description: |-
                             The LoadBalancer-type Service provider to deploy. Not required in infrastructures where

api/v1alpha1/crds/caren.nutanix.com_nutanixclusterconfigs.yaml

@@ -218,6 +218,31 @@ spec:
                       type: object
                     serviceLoadBalancer:
                       properties:
+                        configuration:
+                          description: Configuration for the chosen ServiceLoadBalancer provider.
+                          properties:
+                            addressRanges:
+                              description: |-
+                                AddressRanges is a list of IPv4 address ranges the
+                                provider uses to choose an address for a load balancer.
+                              items:
+                                description: AddressRange defines an IPv4 range.
+                                properties:
+                                  end:
+                                    format: ipv4
+                                    type: string
+                                  start:
+                                    format: ipv4
+                                    type: string
+                                required:
+                                  - end
+                                  - start
+                                type: object
+                              minItems: 1
+                              type: array
+                          required:
+                            - addressRanges
+                          type: object
                         provider:
                           description: |-
                             The LoadBalancer-type Service provider to deploy. Not required in infrastructures where

docs/content/addons/serviceloadbalancer.md

@@ -10,11 +10,15 @@ The Service Load Balancer is the component that backs this Kubernetes Service, e
 a Virtual IP, creating a machine that runs load balancer software, by delegating to APIs, such as
 the underlying infrastructure, or a hardware load balancer.
 
+The Service Load Balancer can choose the Virtual IP from a pre-defined address range. You can use
+CAREN to configure one or more IPv4 ranges. For additional options, configure the Service Load
+Balancer yourself after it is deployed.
+
 CAREN currently supports the following Service Load Balancers:
 
 - [MetalLB]
 
-## Example
+## Examples
 
 To enable deployment of MetalLB on a cluster, specify the following values:
 
@@ -33,7 +37,30 @@ spec:
               provider: MetalLB
 ```
 
-See [MetalLB documentation] for details on configuration.
+To enable MetalLB, and configure two address IPv4 ranges, specify the following values:
+
+```yaml
+apiVersion: cluster.x-k8s.io/v1beta1
+kind: Cluster
+metadata:
+  name: <NAME>
+spec:
+  topology:
+    variables:
+      - name: clusterConfig
+        value:
+          addons:
+            serviceLoadBalancer:
+              provider: MetalLB
+              configuration:
+                addressRanges:
+                - start: 10.100.1.1
+                  end: 10.100.1.20
+                - start: 10.100.1.51
+                  end: 10.100.1.70
+```
+
+See [MetalLB documentation] for more configuration details.
 
 [external load balancer]: https://kubernetes.io/docs/tasks/access-application-cluster/create-external-load-balancer/
 [MetalLB]: https://metallb.org