Only permit upgrades from 4.12

What does this MR do?

Sets the min upgrade from version to be 4.12 and GitLab 13.12

In order to upgrade, users must be a version on or newer than that.

Test plan

(Note that the check does not run for non-semver versions)

1. Install a previous release version of the chart pre-4.12.
2. Check this branch, and modify your top-level Chart.yml file to be semver values
   • appVersion should be 14.0.0
   • version should be 5.0.0
3. Attempt to upgrade to the local version
   • The upgrade should fail, and the upgrade status pod termination message should have the expectet reason
4. Upgrade to the release version of 4.12
   • This should succeed
5. Attempt the update to the local version again
   • This should now succeed

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

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 omnibus-gitlab opened