Allow admins to make specific project services unavailable
Description
An administrator may wish to disable the use of certain project services globally, or for a particular group or project. In particular, the "terminal websocket" support in !7690 (merged) may need disabling in some contexts.
Proposal
Extend service templates so the administrator can make some of them unavailable to project owners.
Stretch: Allow their use to be restricted to a whitelist or blacklist of names (by user, group or project).