Update az cli command to generate AZURE_CREDENTIALS

[gagofure]

The script to generate AZURE_CREDENTIALS needs to be updated. --sdk-auth is depreciated and no longer required.

New script should look like this

   az ad sp create-for-rbac --name  myApp --role contributor \
                            --scopes /subscriptions/{subscription-id}/resourceGroups/{resource-group} \         

[tonybaloney]

Additionally, --name should be --appId

[ezYakaEagle442]

This doc https://github.com/Azure/actions-workflow-samples/blob/master/assets/create-secrets-for-GitHub-workflows.md should be updated accordignly