addon development guide (#628)

* addon development guide
* include feedback from Kiefer
* renamed addon to add-on to better reflect upcoming ui changes: harvester/dashboard#1110
* Apply suggestions from code review
include feedback for PR review.
Co-authored-by: Jillian <67180770+jillian-maroket@users.noreply.github.com>

* Update docs/developer/addon-development.md
Co-authored-by: Alexandra Settle <asettle@suse.com>

---------
Co-authored-by: Jillian <67180770+jillian-maroket@users.noreply.github.com>
Co-authored-by: Alexandra Settle <asettle@suse.com>

docs/developer/_category_.json

@@ -1,10 +1,6 @@
 {
     "position": 18,
-    "label": "Developer",
-    "collapsible": false,
-    "collapsed": false,
-    "link": {
-        "type": "doc",
-        "id": "developer-mode-installation"
-    }
+    "label": "Development Guides",
+    "collapsible": true,
+    "collapsed": true
 }

docs/developer/addon-development.md

@@ -0,0 +1,67 @@
+---
+id: Add-on-development-guide
+title: "Add-on Development Guide"
+sidebar_position: 1
+sidebar_label: Add-on Development Guide
+keywords:
+  - Harvester
+  - harvester
+  - Add-on Development
+Description: How to write your own Harvester add-on
+---
+
+Harvester add-ons allow you to enable and disable specific Harvester and third-party components based on your requirements. Add-ons function as a wrapper for the [RKE2 HelmChart resource definition (CRD)](https://docs.rke2.io/helm#using-the-helm-crd).
+
+
+## Prerequisites
+
+- An existing Harvester cluster
+
+## Add-on Specifications
+
+The `Addon` CRD supports the following fields:
+
+```yaml
+apiVersion: harvesterhci.io/v1beta1
+kind: Addon                         
+metadata:
+  name: example-add-on           # Name of add-on
+  namespace: example-namespace  # Namespace where the add-on CRD is deployed and where the associated Kubernetes components will be deployed
+  labels:                       # Optional add-on labels
+    Add-on.harvesterhci.io/experimental: "true" # Predefined label used on the Harvester UI to identify add-ons with the "experimental" maturity level
+spec:
+  enabled: false                # Boolean indicating if an add-on should be enabled or disabled on definition
+  repo: https://chartsrepo.com  # Helm chart repository containing the Helm chart managed by the add-on
+  version: "v0.19.0"            # Version of the Helm chart to be installed
+  chart: mychart                # Name of the Helm chart in the Helm chart repository
+  valuesContent: |-             # File (values.yaml) that must be passed to the Helm chart
+    contents of values.yaml
+    that need to be passed
+    to the chart
+```
+
+:::note
+
+Experimental add-ons are not directly packaged in Harvester. An example is the [rancher-vcluster](https://github.com/harvester/experimental-addons/blob/main/rancher-vcluster/rancher-vcluster.yaml) add-on.
+
+:::
+
+## Installation
+
+```bash
+kubectl apply -f /path/to/add-on.yaml
+```
+
+## Usage
+
+After creating an `Addon` CRD, you can can toggle the `enabled` field to enable and disable the associated Helm chart.
+
+## Upgrade
+
+Changes to the `repo`, `version`, `chart` or `valueContent` fields will trigger a `helm upgrade`, which forces an upgrade of the existing Helm chart.
+
+## Uninstallation
+
+```bash
+kubectl delete -f /path/to/Add-on.yaml
+```