The `services.mastodon` module currently hardcodes sidekiq's concurrency
to 25, but doesn't set a DB pool size, which defaults to 5 or the number
of configured web threads.
(This behaviour is very strange, and arguably a mastodon bug.)
This also makes sidekiq's concurrency configurable, because 25 is a tad
high for the hardware I'm running it on.
(cherry picked from commit e8fd7792d1eeb4ea4943cc34525da1159ab50bc9)
4255954d972a67d2e50104cb4c72a0f22e1234dd set the StateDirectory to 0750,
but nginx wasn't in the Mastodon group. This commit also deletes a line,
that probably was intended to serve this purpose, but makes no sense.
Why should the Mastodon user be added as an extraGroup to the nginx
user?
