Demonstrate image retrieval and produce mock images for testing within the RSP

[talister]

The ability to query Rubin services for images of 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 images (or smaller postage stamps if full images are too large (>200MB?)) that are comparable to Rubin images should also be demonstrated for future use in tests. (Possible sources of suitable images could be DP0.2 (if permitted to be committed to external repos), the rc2_subset or generated by Stuff)

[mschwamb]

Agreement in the call this week to use the obscore table