Allow permissions on specific fields in hasura actions

### Is your proposal related to a problem?

We execute an action and we want to be able to filter the result via permissions. Currently we are only able to set a general "Allowed" or "Not Allowed" check on the complete action, but it would be pretty good if we could have the same fine grained permissions as we have on a DB table.

The problem with this is that we now move this action into our backend to do the filtering ourselves, but this is something which should be possible in hasura.

### Describe the solution you'd like

Example would be:

1. Execute an action
2. Set permission on this action so that a user is only able to see data entries when a column has value X (which we get from the hasura session).

The issue names no files, tests, or entry points. Start by locating Hasura action permission handling and compare it with existing database-table permissions, then determine how session-derived conditions could apply to selected fields. Done means actions support field-level filtering based on permission rules rather than only an action-wide allow or deny.

Written by the indexing model from the issue text.