GraphQL JSON type filter options

Along the lines of #882
Wanted to keep the discussions separate so I opened a separate issue, but the question remains the same. What filter options should be provide for JSON type.

E.g. Postgres has pretty good json support: https://www.postgresql.org/docs/current/functions-json.html
So we can consider adding filtering options like json-s with key "a".

Start by reading issue #882 and the PostgreSQL JSON functions documentation linked here. No implementation file, entry point, or test is named; the work would first require deciding which JSON filter options the GraphQL API should support and defining how completion would be verified.

Written by the indexing model from the issue text.