[Service Bus extension] ServiceBusScalerProvider does not clean up resources

[JoshLove-msft]

The ServiceBusScalerProvider constructs a ServiceBusClient and ServiceBusReceiver and passes these into ServiceBusTargetScaler.
ServiceBusTargetScaler passes these into ServiceBusMetricsProvider where the receiver is used periodically to peek messages from the queue. There are no lifecycle methods on the ServiceBusScalerProvider and the ServiceBusClient never gets closed. This leads to test failures like https://dev.azure.com/azure-sdk/internal/_build/results?buildId=2928991&view=ms.vss-test-web.build-test-results-tab&runId=42025520&resultId=101117&paneView=debug. There should be a method that is called as part of the ServiceBusScalerProvider lifetime that allows it to be cleaned up.

The ServiceBusTargetScaler also is added via the ServiceBusListener, but this is not a problem as the underlying ServiceBusClient is closed when the ServiceBusListener is closed.