Remove struct tags from Inventory

We don't really care how these fields are serialized (as long as they
are serialized), it's also less work when we decide to add/remove a
field.

e2e/internal/command/testdata/TestInventory/inventory_from_template_created

@@ -1,9 +1,9 @@
 ip: 100.100.100.100
-vm_id: /subscriptions/uuid/resourceGroups/rg/providers/Microsoft.Compute/virtualMachines/some_vm_id
+vmid: /subscriptions/uuid/resourceGroups/rg/providers/Microsoft.Compute/virtualMachines/some_vm_id
 uuid: 1fb2b697-c271-4aa8-aeb6-2a5f5bde5edd
-vm_name: adsys-e2e-lunar-1fb2b697-c271-4aa8-aeb6-2a5f5bde5edd
+vmname: adsys-e2e-lunar-1fb2b697-c271-4aa8-aeb6-2a5f5bde5edd
 codename: mantic
 state: base_vm_created
-ssh_key_path: /home/user/.ssh/id_rsa
+sshkeypath: /home/user/.ssh/id_rsa
 hostname: ""
-base_vm_image: ""
+basevmimage: ""

e2e/internal/inventory/inventory.go

@@ -13,15 +13,15 @@ const DefaultPath = "inventory.yaml"
 
 // Inventory represents the contents of an inventory file.
 type Inventory struct {
-	IP          string `yaml:"ip"`
-	VMID        string `yaml:"vm_id"`
-	UUID        string `yaml:"uuid"`
-	VMName      string `yaml:"vm_name"`
-	BaseVMImage string `yaml:"base_vm_image"`
-	Codename    string `yaml:"codename"`
-	State       State  `yaml:"state"`
-	SSHKeyPath  string `yaml:"ssh_key_path"`
-	Hostname    string `yaml:"hostname"`
+	IP          string
+	VMID        string
+	UUID        string
+	VMName      string
+	BaseVMImage string
+	Codename    string
+	State       State
+	SSHKeyPath  string
+	Hostname    string
 }
 
 // Write writes the inventory file to the given path.