Print PG11 deprecation notice

What does this MR do?

Prints a deprecation notice for PG11 per #5499 (closed).

Related issues

Closes #5499 (closed)

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion

Required

• Merge Request Title, and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com
• Pipeline is green on dev.gitlab.org if the change is touching anything besides documentation or internal cookbooks
• trigger-package has a green pipeline running against latest commit

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for the GitLab Chart opened

Testing

apt-get update / gitlab-ctl upgrade

gitlab Reconfigured!
Restarting previously running GitLab services
ok: run: alertmanager: (pid 16702) 1s
ok: run: gitaly: (pid 1552) 4847s
ok: run: gitlab-exporter: (pid 16713) 0s
ok: run: gitlab-workhorse: (pid 16715) 0s
ok: run: grafana: (pid 16730) 1s
ok: run: logrotate: (pid 16742) 0s
ok: run: nginx: (pid 16748) 1s
ok: run: node-exporter: (pid 16758) 0s
ok: run: postgres-exporter: (pid 16760) 0s
ok: run: postgresql: (pid 609) 5042s
ok: run: prometheus: (pid 16774) 0s
ok: run: puma: (pid 16776) 0s
ok: run: redis: (pid 436) 5054s
ok: run: redis-exporter: (pid 16789) 0s
ok: run: sidekiq: (pid 16799) 1s

     _______ __  __          __
    / ____(_) /_/ /   ____ _/ /_
   / / __/ / __/ /   / __ `/ __ \
  / /_/ / / /_/ /___/ /_/ / /_/ /
  \____/_/\__/_____/\__,_/_.___/


Upgrade complete! If your GitLab server is misbehaving try running
  sudo gitlab-ctl restart
before anything else.
If you need to roll back to the previous version you can use the database
backup made during the upgrade (scroll up for the filename).

=== INFO ===
Note that PostgreSQL 12 will become the minimum required PostgreSQL version in GitLab 14.0 (May 2021).
PostgreSQL 11 will be removed in GitLab 14.0. Please consider upgrading your PostgreSQL version soon.
https://docs.gitlab.com/omnibus/settings/database.html#upgrade-packaged-postgresql-server
=== INFO ===

Closes #5499 (closed)