Add /query/list/parents endpoint

[albireox]

Adds a new /query/list/parents endpoint which returns the list of catalogdb tables that are referenced from sdss_id_to_catalogs.

>> curl -L "http://127.0.0.1:8000/query/list/parents"                                                                              
["allstar_dr17_synspec_rev1","allwise","bhm_rm_v0","bhm_rm_v0_2","catwise","catwise2020","gaia_dr2_source","gaia_dr3_source","glimpse","guvcat","legacy_survey_dr10","legacy_survey_dr8","panstarrs1","ps1_g18","sdss_dr13_photoobj","skymapper_dr1_1","skymapper_dr2","supercosmos","tic_v8","twomass_psc","tycho2","unwise"]

Not sure about the parents segment of the route. I used parents to be symmetric with #38 but it could also be catalogs.

Closes #39.

[havok2063]

Looks good to me.