API improvement: /v1/artefacts should have more filters

`GET /v1/artefacts` can only filter on artifact `family`. It would be nice to be able to filter on more fields depending on each artifact type. For example, `family=image` should allow filtering at least on `os`, `release`, `owner`, or `stage`.

Start by locating the implementation of GET /v1/artefacts and how artifact families expose their fields. Define how filters for fields such as os, release, owner, and stage vary by artifact type, then verify that family=image queries return the expected filtered results.

Written by the indexing model from the issue text.