Add setting to limit committee admin's permissions to set others as committee admins

[bspekker]

Current behavior
Currently the committee admin can add (and edit) committee admins to their own committee. This is not always intended.

Wanted behavior

• A new setting is needed for orga admins so that committee admins will no longer be able to edit the “Committee managers” field in their respective top-level committees. By default the setting should not be checked. Wording of the setting: Restrict editing of committee admins to subcommittees, orga admins will not be restricted.
• If the setting is activated, only organ admins will be able to edit all committee managers. Committee admins will then only be able to appoint/remove committee admins in their subcommittees.

Additional context
Wording of setting may change in final version.