Add fake queue and job tracking in Armada Client mock server

[richscott]

The Scala Armada client server mocks in ArmadaClientSuite.scala have methods for creating, querying, and deleting queues and jobs, but they don't actually track them internally - they usually just return a successful (empty) response. However, in an actual Armada cluster, if you, for example, call getQueue with the name of a queue that was never actually created before (by using createQueue), it will return a GRPC exception. The same will happens with jobs.

For greater fidelity to actual Armada behavior, the mocks should just track queue & job creation by using simple internal maps, and then the mock should return appropriate exceptions as like what Armada does right now. Any deeper Armada functionality of queues & jobs is probably not needed, we just need to track creation/deletion, via maps of the basic Queue & Job objects.