Make IManagementApiClient implement IDisposable

[kevbite]

We currently have a factory that creates us IManagementApiClient based on different inputs, however, it does not implement IDisposable, only the concrete class which means that the class outside of that creating the instance via the factory cannot dispose of the IManagementApiClient.

 using IManagementApiClient managementApiClient = await _managementApiClientFactory.CreateManagementApiClient(things);