Validate azure monitor metric alerts

[jplane]

Validate whether/how azure monitor metric alerts can implement the following scenario (and similar):

"invoke a webhook whenever the avg CPU across all container groups within resource group X is > 75"

• can you configure this thru CLI, .NET SDK, REST?
• can you scope it to the resource group so that you don't have to modify the alert each time you add/remove a container group?
• will the alert compute and evaluate a single average across all CGs within a given RG? or will it merely evaluate each separately? (we want the former, not the latter)

Relevant links:

hashicorp/terraform-provider-azurerm#4337

https://github.com/Azure/azure-libraries-for-net/blob/master/Tests/Fluent.Tests/Monitor/MonitorTests.cs#L614