* Align ActorSnapshot/ActorSnapshotTag store methods to other CRUD
methods.
* Add common struct types for List<Type> methods to carry parameters and
returned pages.
* Sort methods in store interface to group methods for each resource.
* Remove pessimistic locking from ActorSnapshot/ActorSnapshotTag RPC
handlers.
* Align CreateActorSnapshotTag method to API guideline. It should take
just the resource, no extra top level field.