Column Presets for delete

Assume a `TABLE favorites (some_id, user_id, PRIMARY KEY(some_id, user_id))`.

A normal user is only allowed to set favorites with their own user id, therefore on INSERT there is a column preset forcing `user_id` to `X-Hasura-User-Id`.

Now, to remove the favorite, a mutation DELETING the record is issued (e.g. `delete_by_pk`). But here, awkwardly, the `user_id` has to be provided (or, the existing record has to be known (SELECT), if it would include an addition `id` column as pk), although it can only have one value (X-Hasura-User-Id, which is known by hasura), because the DELETE permission does not support column presets...

The issue names no files or tests; start by tracing DELETE permission handling and comparing it with the existing INSERT column-preset behavior described here. Done means a delete mutation can apply the authenticated user's ID without requiring that ID as an input or an additional lookup.

Written by the indexing model from the issue text.