Azure Stack Hub HybridEnvironment Support

[patrickdillon]

/kind feature

Describe the solution you'd like
Support using CAPZ to provision clusters on Azure Stack Hub.

Anything else you would like to add:
Achieving this goal would entail:

• Adding Azure Stack Cloud (or HybridEnvironment) as a valid AzureEnvironment
• Configuring cloud endpoints for the azure stack environment
• Adding support for Basic Load Balancers (only supported LB on Azure Stack Hub)
• Updating API version to a compatible profile as necessary (I believe this is only needed for resources that are not provisioned using ASO, so we can either migrate them to ASO or update the profiles. I'm currently working through NSGs, not sure if more are needed).

Environment:

• cluster-api-provider-azure version:
• Kubernetes version: (use kubectl version):
• OS (e.g. from /etc/os-release):

[nojnhuh]

FYI @mboersma I think this will probably intersect with #4780.

I see ASO exposes only the AZURE_AUTHORITY_HOST, AZURE_RESOURCE_MANAGER_ENDPOINT, and AZURE_RESOURCE_MANAGER_AUDIENCE variables instead what CAPZ does now with the pre-baked sets of those for public cloud, China, Gov cloud, etc. @patrickdillon Would a way to set the equivalents of those variables in CAPZ be sufficient?

And since CAPZ would ultimately have to pass this config along to ASO, we should iron out Azure/azure-service-operator#3447 first before we commit to any API changes in CAPZ.