ACR audience should be optional with a default value, and not required

[lmazuel]

Today we need to write:

client = ContainerRegistryClient(end_point, DefaultAzureCredential(), audience="https://management.azure.com")

Audience should be optional. Please check the right default in other languages.

[YalinLi0312]

Will update until we have a default ACR audience from the service.

[pallavit]

I vaguely remember this was a conscious call we had made at the time but I do not recollect the reason :|. I believe some of our SDKs today do have a default especially for national cloud support does it makes sense for us to do the same for ACR as well?
/cc: @annelo-msft , @lmolkova

[lmolkova]

ACR for Java defaults to public cloud. But it's required on .NET (it was introduced here Azure/azure-sdk-for-net#23141, it seems there was a need to postpone choosing default value).

BTW I never saw another SDK that requires an audience, so let's try to make it optional unless there is a strong reason not to. And of course, make it consistent.

[lmolkova]

Found the guideline: https://azure.github.io/azure-sdk/policies_support.html#azure-clouds

By default, the Azure libraries are configured to connect to the Global Azure Cloud.