Get permission service: clean "can_request_help" usage

[smadbe]

Motivations

The current spec of the service does not really work how the "can_request_help" is designed. So let's fix it.

Subtasks

• in computed and all granted_via_*, can_request_help_to is aggregate of several groups, so return an array of the (id, is_all_users_group, name) tuple. This should be [] is there is no such groups.
• in granted, the can_request_help_to is unique to keep (id, is_all_users_group, name). can_request_help_to should be null if there is no value set.
• In both cases, if a group is not visible by the current user, the name should not be given, but the id or is_all_users_group should be given in any case.