doc: improve Clusters Azure API type documentation

Improve the documentation for different attributes in the
Azure section of the Clusters API type.

Specifically:
- clarified whether some of the resources associated
  to the attributes must exist beforehand or not
- Indicate whether the attribute is required during
  creation or not
- Indicate whether the attribute can be updated or
  not (immutability)

The documentation reflects the current behavior. It is
possible that in the future some of the aspects of them
regarding immutability and/or optionality might change.

model/clusters_mgmt/v1/azure_type.model

@@ -16,37 +16,49 @@ limitations under the License.
 
 // Microsoft Azure settings of a cluster.
 struct Azure {
-	// [Required] The Azure Subscription ID associated with the cluster. It must belong to
+	// The Azure Subscription ID associated with the cluster. It must belong to
 	// the Microsoft Entra Tenant ID `tenant_id`.
+	// Required during creation.
+	// Immutable.
 	SubscriptionID           String
 
-	// [Required] The Azure Resource Group Name of the cluster. It must be within `subscription_id`
-	// of the cluster. `resource_group_name` is located in the same Azure location
-	// as the cluster's region.
+	// The Azure Resource Group Name of the cluster. It must be a pre-existing
+	// Azure Resource Group and it must exist within the Azure Subscription
+	// `subscription_id` of the cluster.
+	// `resource_group_name` is located in the same Azure location as the
+	// cluster's region.
+	// Required during creation.
+	// Immutable.
 	ResourceGroupName        String
 
-	// [Required] The Azure Resource Name of the cluster. It must be within the
+	// The Azure Resource Name of the cluster. It must be within the
 	// Azure Resource Group Name `resource_group_name`.
 	// `resource_name` is located in the same Azure location as the cluster's region.
+	// Required during creation.
+	// Immutable.
 	ResourceName             String
 
-	// [Required] The Microsoft Entra Tenant ID where the cluster belongs.
+	// The Microsoft Entra Tenant ID where the cluster belongs.
+	// Required during creation.
+	// Immutable.
 	TenantID                 String
 
-	// [Required] The name of the Azure Resource Group where the Azure Resources related
-	// to the cluster are created. The Azure Resource Group is created with the given
-	// value, within the Azure Subscription `subscription_id` of the cluster.
+	// The desired name of the Azure Resource Group where the Azure Resources related
+	// to the cluster are created. It must not previously exist. The Azure Resource
+	// Group is created with the given value, within the Azure Subscription
+	// `subscription_id` of the cluster.
 	// `managed_resource_group_name` cannot be equal to the value of `managed_resource_group`.
 	// `managed_resource_group_name` is located in the same Azure location as the
 	// cluster's region.
 	// Not to be confused with `resource_group_name`, which is the Azure Resource Group Name
 	// where the own Azure Resource associated to the cluster resides.
+	// Required during creation.
+	// Immutable.
 	ManagedResourceGroupName String
 
-	// [Required] The Azure Resource ID of a pre-existing Azure
-	// Subnet. It is an Azure Subnet used for the Data Plane of the cluster.
-	// `subnet_resource_id` must be located in the same Azure location as the
-	// cluster's region.
+	// The Azure Resource ID of a pre-existing Azure Subnet. It is an Azure
+	// Subnet used for the Data Plane of the cluster. `subnet_resource_id`
+	// must be located in the same Azure location as the cluster's region.
 	// The Azure Subscription specified as part of the `subnet_resource_id`
 	// must be located in the same Azure Subscription as `subscription_id`.
 	// The Azure Resource Group Name specified as part of `subnet_resource_id`
@@ -58,10 +70,11 @@ struct Azure {
 	// The Azure Resource Group Name specified as part of the `subnet_resource_id`
 	// can be the same, or a different one than the one specified in
 	// `resource_group_name`.
+	// Required during creation.
+	// Immutable.
 	SubnetResourceID String
 
-	// [Required] The Azure Resource ID of a pre-existing
-	// Azure Network Security Group.
+	// The Azure Resource ID of a pre-existing Azure Network Security Group.
 	// The Network Security Group specified in network_security_group_resource_id
 	// must already be associated to the Azure Subnet `subnet_resource_id`.
 	// It is the Azure Network Security Group associated to the cluster's subnet
@@ -80,5 +93,7 @@ struct Azure {
 	// The Azure Resource Group Name specified as part of `network_security_group_resource_id`
 	// can be the same, or a different one than the one specified in
 	// `resource_group_name`.
+	// Required during creation.
+	// Immutable.
 	NetworkSecurityGroupResourceID String
 }