Remove Pgvector - part 1

What does this MR do and why?

We're no longer using pgvector. So the first part will involve creating docker images with postgres versions 12-18 only.

The rest of the upcoming parts:

• Part 2 - Reference the new docker images with postgres only in the gitlab repo and remove all traces of pgvector
• Part 3 - Delete the docker postgres pgvector images from this repo

See discussion here: !1020 (comment 2838691718)

Checklist

• (If applicable) Add patches if required for upgrading Ruby version in https://gitlab.com/gitlab-org/gitlab-build-images/-/tree/master/patches/ruby.