Add native systemd units

This commit adds native systemd units for the source installation as an
alternative to the current init script.

The units are:
- Service files can be used to seperately start and stop the individual
  GitLab daemons and the target.
- A target unit to logically group the individual services and to start
  and stop GitLab as a whole.
- A slice unit for resource monitoring.

Changelog: added

lib/support/systemd/gitlab-gitaly.service

+[Unit]
+Description=GitLab Gitaly
+ReloadPropagatedFrom=gitlab.target
+PartOf=gitlab.target
+After=network.target gitlab-puma.service
+
+[Service]
+Type=simple
+User=git
+WorkingDirectory=/home/git/gitlab
+ExecStart=/home/git/gitaly/_build/bin/gitaly /home/git/gitaly/config.toml
+Restart=on-failure
+SyslogIdentifier=gitlab-gitaly
+Slice=gitlab.slice
+
+[Install]
+WantedBy=gitlab.target

lib/support/systemd/gitlab-mailroom.service

+[Unit]
+Description=GitLab Mailroom
+PartOf=gitlab.target
+After=network.target
+StartLimitIntervalSec=100s
+
+[Service]
+Type=simple
+User=git
+WorkingDirectory=/home/git/gitlab
+Environment=RAILS_ENV=production
+ExecStart=/usr/local/bin/bundle exec mail_room --log-exit-as json --quiet --config /home/git/gitlab/config/mail_room.yml
+Restart=on-failure
+RestartSec=1
+SyslogIdentifier=gitlab-mailroom
+Slice=gitlab.slice
+
+[Install]
+WantedBy=gitlab.target

lib/support/systemd/gitlab-pages.service

+[Unit]
+Description=GitLab Pages
+ReloadPropagatedFrom=gitlab.target
+PartOf=gitlab.target
+After=network.target gitlab-puma.service
+Wants=gitlab-puma.service
+
+[Service]
+Type=simple
+User=git
+WorkingDirectory=/home/git/gitlab
+ExecStart=/home/git/gitlab-pages/gitlab-pages -config /home/git/gitlab-pages/gitlab-pages.conf
+Restart=on-failure
+RestartSec=1
+SyslogIdentifier=gitlab-pages
+Slice=gitlab.slice
+
+[Install]
+WantedBy=gitlab.target

lib/support/systemd/gitlab-puma.service

+[Unit]
+Description=GitLab
+Conflicts=gitlab.service
+ReloadPropagatedFrom=gitlab.target
+PartOf=gitlab.target
+# # You might want to add these if you run redis and postgres on the same
+# # machine as gitlab. Do this by either uncommenting the following `Requires=`
+# # and `After=` or, preferedly, running `systemctl edit gitlab-puma.service`
+# # and adding a `[Unit]` section and the respective keys below it.
+# Requires=redis-server.service postgresql.service
+# After=redis-server.service postgresql.service
+After=network.target
+StartLimitIntervalSec=100s
+
+[Service]
+Type=notify
+User=git
+WorkingDirectory=/home/git/gitlab
+Environment=RAILS_ENV=production
+ExecStart=/usr/local/bin/bundle exec puma --config /home/git/gitlab/config/puma.rb --environment production --pidfile /home/git/gitlab/tmp/pids/puma.pid
+ExecReload=/usr/bin/kill -USR2 $MAINPID
+PIDFile=/home/git/gitlab/tmp/pids/puma.pid
+# puma can be slow to start
+TimeoutStartSec=120
+WatchdogSec=10
+Restart=on-failure
+RestartSec=1
+SyslogIdentifier=gitlab-puma
+Slice=gitlab.slice
+
+[Install]
+WantedBy=gitlab.target

lib/support/systemd/gitlab-sidekiq.service

+[Unit]
+Description=GitLab Sidekiq
+ReloadPropagatedFrom=gitlab.target
+PartOf=gitlab.target
+After=network.target
+# # You might want to add these if you run redis and postgres on the same
+# # machine as gitlab. Do this by either uncommenting the following `Requires=`
+# # and `After=` or, preferedly, running `systemctl edit gitlab-puma.service`
+# # and adding a `[Unit]` section and the respective keys below it.
+# Wants=redis-server.service postgresql.service
+# After=redis-server.service postgresql.service
+JoinsNamespaceOf=gitlab-puma.service
+
+[Service]
+Type=simple
+User=git
+WorkingDirectory=/home/git/gitlab
+Environment=RAILS_ENV=production
+ExecStart=/usr/local/bin/bundle exec sidekiq --config /home/git/gitlab/config/sidekiq_queues.yml --environment production
+ExecStop=/usr/local/bin/bundle exec sidekiqctl stop /run/gitlab/sidekiq.pid
+PIDFile=/home/git/gitlab/tmp/pids/sidekiq.pid
+Restart=on-failure
+RestartSec=1
+SyslogIdentifier=gitlab-sidekiq
+Slice=gitlab.slice
+
+[Install]
+WantedBy=gitlab.target

lib/support/systemd/gitlab-workhorse.service

+[Unit]
+Description=GitLab Workhorse
+ReloadPropagatedFrom=gitlab.target
+PartOf=gitlab.target
+After=network.target gitlab-puma.service
+Wants=gitlab-puma.service
+
+[Service]
+Type=simple
+User=git
+WorkingDirectory=/home/git/gitlab
+Environment=PATH=/home/git/gitlab-workhorse:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+ExecStart=/home/git/gitlab-workhorse/gitlab-workhorse  -listenUmask 0 -listenNetwork unix -listenAddr /home/git/gitlab/tmp/sockets/gitlab-workhorse.socket -authBackend http://127.0.0.1:8080 -authSocket /home/git/gitlab/tmp/sockets/gitlab.socket -documentRoot /home/git/gitlab/public -secretPath /home/git/gitlab/.gitlab_workhorse_secret
+ExecReload=/usr/bin/kill -USR2 $MAINPID
+Restart=on-failure
+RestartSec=1
+SyslogIdentifier=gitlab-workhorse
+Slice=gitlab.slice
+
+[Install]
+WantedBy=gitlab.target

lib/support/systemd/gitlab.slice

+[Unit]
+Description=Slice to bundle all GitLab services
+Before=slices.target
+
+[Slice]
+MemoryAccounting=true
+IOAccounting=true
+CPUAccounting=true

lib/support/systemd/gitlab.target

+[Unit]
+Description=GitLab
+Wants=gitlab-gitaly.service gitlab-puma.service gitlab-sidekiq.service gitlab-workhorse.service
+
+[Install]
+WantedBy=multi-user.target