In GitLab EE, a GitLab instance can be read-only (e.g. when it's a Geo
secondary node). But in GitLab CE it also might be useful to have the
"read-only" idea around. So port it back to GitLab CE.
Also having the principle of read-only in GitLab CE would hopefully
lead to less errors introduced, doing write operations when there
aren't allowed for read-only calls.
Closes gitlab-org/gitlab-ce#37534.
This makes things simpler as no scheduling is involved. Further we
remove the need for running a SELECT + UPDATE just to get the key and
update it, whereas we only need an UPDATE when setting last_used_at
directly in a request.
The added service class takes care of updating Key#last_used_at without
using Sidekiq. Further it makes sure we only try to obtain a Redis lease
if we're confident that we actually need to do so, instead of always
obtaining it. We also make sure to _only_ update last_used_at instead of
also updating updated_at.
Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/36663
