ENH: have a way to list collections for query_sia

[bsipocz]

E.g. in the Irsa module we have a list_catalogs, but it returns the TAP schemas rather than what the collection keyword for SIA would expect (e.g. spitzer.seip_images vs spitzer_seip)

(This is me trying to figure out how to e.g. query for WISE images from a user's POV who doesn't know the collection name already, etc.)

[bsipocz]

Ways to do this:

the most up-to-date way to find a list of SIAv2 collections is by calling https://irsa.ipac.caltech.edu/SIA?maxrec=0&responseformat=votable and looking at  values of the COLLECTION param.

https://irsa.ipac.caltech.edu/TAP/sync?QUERY=select%20distinct%20collection%20from%20caom.observation%20order%20by%20collection&format=html

where we do have it cached for HTML, ipac table and json, but it will need astropy/pyvo#524 to be able to do so in astroquery