(PDB-1028) Make /v4/catalogs queryable

This expands the /v4/catalogs endpoint to have full query and paging capacity,
and brings the catalogs endpoint into the query engine like the others, which
will be useful for syncing and future consistency. This patch changes the /v4/catalogs response to be a list and changes the response schema to include a hash key.
thought I responded to this the other day -- guess not.  That's so the v3 endpoint can be restricted with a normal query, but it's overkill and the regex compilation below is not even necessary.  Happy to get rid of it.  Should we just 404 for /v3/catalogs/host then?