Prepare-Release should handle being logged into the non-public cloud

Here https://github.com/Azure/azure-sdk-tools/blob/main/eng/common/scripts/Update-DevOps-Release-WorkItem.ps1#L26 we should detect which cloud we are logged into (`az account show --query environmentName` or `az cloud show --query name`) and if it isn't the public `AzureCloud` we should output an error message telling folks. The error message should tell them how to switch clouds `az cloud set --name AzureCloud`. While we could consider doing this for them automatically, I don't want to disrupt any other potential workflows on the system given this is user wide state. We will let the user change that state.

The reason this is needed is because the azure-devops extension can only get a token against the public cloud.