Add a check for remote pg_version in order to print deprecation messages

What does this MR do?

Add a check for remote pg_version in order to print deprecation messages

Grabs the pg-version from the rails environment. Only runs on nodes that run migrations to ensure we know these nodes can connect to the DB.

Only runs when migrations run, as not to add as much additional rails overhead to reconfigure. But it should run on each upgrade for the migration node.

Related issues

#5500 (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