POC to manually configure alternate audiences for AAD

[TimothyMothra]

This PR is a Proof of Concept to support configuring alternate audiences for AAD. I'm using this as a conversation starter.

How to use:

var config = new TelemetryConfiguration
{
    ConnectionString = "..."
}
var credential = new DefaultAzureCredential();
config.SetAzureTokenCredential(
    tokenCredential: credential,
    audience: AzureMonitorAudience.AzurePublicCloud);