[Bugbash][azure-sdk-for-csharp]Missing Client Builder extensions for AAD

[terencefan]

Describe the bug

There should be a client extension like this:

services.AddAzureClients(builder =>
{
    builder.AddWebPubSubServiceClient<TBuilder>(this TBuilder builder, Uri endpoint, string hub, TokenCredential credential)
}

But we only have AzureKeyCredential version for accesskey auth method now.

To Reproduce

Exceptions (if any)

Further technical details