[ACR] Do not require audience on ClientOptions

[annelo-msft]

@lmolkova is working with the service team to understand whether we will need to continue requiring callers to pass Audience into ACR clients, or whether we can set a default of "https://containerregistry.azure.net".

Once this is decided, implement the decided outcome.

[lmolkova]

Based on the information from the service team, we should proceed with defaulting to "https://containerregistry.azure.net/" when the audience is not set (for all clouds).

[annelo-msft]

• Update TSG with Java example as well