Service Bus purge / batch delete

[black-snow]

Related command
Apparently there's some batch delete in preview - can we get this in the CLI, please? It'd be super handy to be able to just purge a queue instead of draining it by receiving each message either via the CLI or the GUI.

What I'd like to have: az servicebus queue purge URL

[yonzhan]

Thank you for opening this issue, we will look into it.