Demonstrate catalog query and produce mock catalogs for testing within the RSP

[talister]

The ability to query Rubin services for source catalogs at a specific RA, Dec pointing, at a specific time and in a specific filter, along with a list of other data in different filters, from user code running within the Rubin Science Platform should be demonstrated.
The ability to return mock catalogs that are comparable to Rubin catalogs should also be demonstrated for future use in tests.