Allow meeting user restriction mode E for related user

[bastianjoel]

In #972 there was a comment missed which requested to allow restriction mode to be accessible by the requesting user themselves.

#972 (comment)

[reiterl]

A user with one meeting, which they is locked out, tries to log in.
=> In the operator:subscription the autoupdate service delivers one meeting_user object, but this doesn't include the 'meeting_id'. So the meeting_user object cannot be used in the code (e.g. to get the locked_out boolean).

[reiterl]

@bastianjoel please look at it.

[bastianjoel]

I think the best way to solve this is to add a new restriction mode to meetings E, for the field meeting_user_ids which is the same as B but allows locked out users.

On the other hand I think we don't necessarily need the meeting id in the client.

[bastianjoel]

I solved this in the client.

[ostcar]

@bastianjoel what is the status of this? Can this me merged or are you waiting for something?

[bastianjoel]

I am currently waiting if OpenSlides/openslides-client#3815 needs additional requirements.