Lack of Method to Retrieve Providers_RegisterAtManagementGroupScope State

When we need to register a provider (e.g. `Microsoft.Network`) to a Subscription, we first call POST method (https://github.com/Azure/azure-rest-api-specs/blob/25bfafa4fc73bb7e876dd5ef00f19b9aa9ba628a/specification/resources/resource-manager/Microsoft.Resources/stable/2022-09-01/resources.json#L2131-L2137), then we can call (https://github.com/Azure/azure-rest-api-specs/blob/25bfafa4fc73bb7e876dd5ef00f19b9aa9ba628a/specification/resources/resource-manager/Microsoft.Resources/stable/2022-09-01/resources.json#L2262-L2268) to retrieve the provider registration state (e.g. `Registered` or `Registering`). But if we want to register the provider at Management Group scope, only the register method is provided. Lack of method to retrieve the registration state and method to unregister the resource provider of the Management Group. This blockes the automation when a resource creation at Management Group scope depends on the resource provider registration.
## Swagger
https://github.com/Azure/azure-rest-api-specs/blob/25bfafa4fc73bb7e876dd5ef00f19b9aa9ba628a/specification/resources/resource-manager/Microsoft.Resources/stable/2022-09-01/resources.json#L2053-L2060

Start with specification/resources/resource-manager/Microsoft.Resources/stable/2022-09-01/resources.json, especially the management-group registration lines 2053-2060 and subscription provider-operation lines 2131-2137 and 2262-2268. Compare the available management-group operations with the subscription registration-state and unregister behavior. Done means the management-group API exposes ways to retrieve registration state and unregister a resource provider.

Written by the indexing model from the issue text.