Check for a covering index using pg_catalog params, not ix name/string matching

[olirice]

Currently vecs uses string pattern matching on the index name to determine if an index exists and supports the correct vector ops

Logic is here https://github.com/supabase/vecs/blob/cc412ce43b525486e8b4e1c376f71227fc1ef5c2/src/vecs/collection.py#L623-L677

It would be preferable to lookup the supported ops in pg_catalog such that it is more intuitive