Previously the Housekeeping button and API would use the counter of last
pushes to determine whether to do a full garbage collection, or whether
to do one of the less comprehensive tasks: a full repack, incremental
pack, or ref pack. This was confusing behavior, since a project owner
might have to click the button dozens of times before a full GC would be
initiated.

This commit forces a full GC each time this is initiated. Note that the
`ExclusiveLease` in `HousekeepingService` prevents users from clicking
on the button more than once a day.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/63349