Relaxed RLS rules to allow access/modify (especially) context table by tightly correlated roles

Especially useful for complex applications (like HAF-BE) where one smaller app is embedded into big one. Then, while using functions like i.e. hive.app_next_block( _context_names hive.contexts_group ) having permission to modify also subcontext data will simplify reusing code specific to embedded app, because its data can be defined using its dedicated role (i.e. btracker_owner) instead of common one (hafbe_owner). Of course hafbe_owner role has granted rights to impersonate as btracker_owner.