Print a deprecation notice for upgrades

Summary

In GitLab 12.10, PostgreSQL 11 will become the default version for upgrades. A user can still opt to stay on PostgreSQL 9.6 or 10 during the upgrade, but if they do, we should warn them that they will need to upgrade PostgreSQL by GitLab 13.0 when PostgreSQL 11 becomes the minimum required version.

Proposal

• On upgrade, if db upgrade is opt out, and PG_VERSION is less than 11, print a warning.
• During reconfigure, if postgresql['version'] is set and less than 11, print a warning.

The warning should read: "Note that PostgreSQL 11 will become the minimum required PostgreSQL version in GitLab 13.0 (May 2020). PostgreSQL 9.6 and PostgreSQL 10 will be removed in GitLab 13.0. Please consider upgrading your PostgreSQL version soon."

Requirements

The notice should print in both of the following cases:

• The user runs sudo apt-get update but opts out of upgrading PostgreSQL
• The user runs sudo gitlab-ctl pg-upgrade but specifies a version other than PostgreSQL 11