create new route for listing parent catalogs

[havok2063]

In connection with #38, we should create a new route under the /query/list section that returns a list of all the available parent catalogs in catalogdb, or at least what is included in catalogdb.sdss_id_to_catalog. This route should have a new response model, which include field descriptions of the parent catalogs.

[albireox]

I can add this one.

When you mention field descriptions for the parent catalogues, do you mean something like this?

[
  {
    "catalog": "gaia_dr3_source",
    "description": "The Gaia catalog, Data Release 3"
  },
  {
    "catalog": "twomass_psc",
    "description": "2MASS Point Source Catalog"
  },
  ...
]

This would essentially mean hardcoding the list of catalogues and descriptions in Valis, although maybe they could be added to the Meta class in the Peewee models.

[havok2063]

I was originally thinking of a pydantic Field(description='') but I don't think that's the right approach here. As part of the response of the endpoint, I think we don't need the descriptions and a simple response list of catalogs is fine.

The table descriptions can come from sdss/sdssdb#263. We already have a valis route for that /info/database. Or alternatively, we could point users to some Wordpress documentation that gets written.

[albireox]

OK. I'll add the route as a simple list of catalog names. I can add metadata for sdss_id_to_catalogs in sdssdb.