[FEATURE] Add Terraform support for azurerm_user_assigned_identity

### Your suggestion

Using `azurerm_user_assigned_identity` along side `azapi` resources is common in Microsoft Learn docs used along side `azurerm_resource_group`.

Let's add support for this resource type because it has a relatively low number of properties that can be configured.

### Alternatives

n/a

### Additional context

- https://learn.microsoft.com/en-us/azure/developer/terraform/get-started-azapi-resource?tabs=azure-cli