Improve test coverage for managed identity scenarios

[danielmarbach]

I have attempted to do a quick spike to setup a managed identity within the setup action

https://github.com/Particular/setup-azureservicebus-action/pull/4

Having something like this in place would enable us to write test scenarios to make sure regression like #700 should no longer happen.

[danielmarbach]

Implemented with https://github.com/Particular/NServiceBus.Transport.AzureServiceBus/pull/993 and https://github.com/Particular/setup-azureservicebus-action/pull/18 as well as https://github.com/Particular/setup-azureservicebus-action/pull/23