Add support for AAD auth to Azure Storage

When migrating from GHES -> GHEC we use Azure Storage as an intermediate storage location for the migration archives. The way we authenticate to Azure Storage today is we require the user to provide an Azure Storage Connection String which includes a shared key.

Some customers would prefer that we use an AAD identity to authenticate instead of a shared key to align with their security policies. We should be able to add support to the CLI to accept a AAD service principal client ID and secret and use that to auth to the storage account.