Link to postgres version table docs

What does this MR do?

There was some confusion in a slack convo in Support for when postgres versions were useable in an Omnibus install.

This adds a link to the package docs Postgres table to the note in the 12.10 specific version changes docs.

Related issues

Slack Convo

Changing the header title?

• Is it completely necessary to change the title? Changing titles breaks deep linking. If yes, proceed further.
• Move the old heading title to the bottom of the page.
• Change the header tag to h5, #####.

Moving docs to a new location?

• Make sure the old link is not removed and has its contents replaced with a link to the new location.
• Make sure internal links pointing to the document in question are not broken.