Support KnownAuthorities across all languages

[jongio]

Right now, when a user wants to work with an alternate cloud they have to specify the authority host in code.

Python has implemented a KnownAuthorties object that allows a user to reference the known other cloud authorities via a const like this:

credential = DefaultAzureCredential(authority=KnownAuthorities.AZURE_GOVERNMENT)

All of the other languages require the user to specify the full url to the known authority, like this:

new EnvironmentCredentialBuilder().authorityHost("https://login.microsoftonline.us/").build()

Ideally, we are consistent across all langs for this.

I have filed issues for the other 4 langs:

JS: Azure/azure-sdk-for-js#7597
.NET: Azure/azure-sdk-for-net#10228
Java: Azure/azure-sdk-for-java#8627
Go: Azure/azure-sdk-for-go#7745

[jongio]

Related: Azure/azure-sdk-for-java#8626 - [FEATURE REQ] Support setAuthorityHost with CredentialBuilderBase #8626

[adrianhall]

Sounds like we should put this in the general guidelines as well, so that future implementors of a new language will take it into consideration. I suspect this belongs in the "azurecore.md" file. Want to take a swag at a PR for this, @jongio?

[jongio]

Will do.

[jongio]

This is now supported in all langs. Thanks team!