Update pause and resume RPCs should accept a job key

Pause and resume RPCs currently accept an update ID, which is a UUID. Scoping these RPCs by JobKey would allow us to change the semantics of the update ID in the future (such that only the JobKey + update ID are universally unique). Adding ownership at the API level will also make it simpler to perform authorization in a cross-cutting way, avoiding a leak of authorization logic into the application layer.