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.

Scritto dal modello di indicizzazione a partire dal testo della issue.