Sync GitLab Pages major and minor versions with main GitLab

Problem

Right now GitLab 15.2.x has a GitLab Pages version 1.61.0: https://gitlab.com/gitlab-org/gitlab/-/blob/15-2-stable-ee/GITLAB_PAGES_VERSION

Every time we backport something for pages, we first go to the above file and see which version backport should target. This is error-prone and makes it harder to reason about pages versions.

Suggestion

Make a leap from 1.61.0 to 15.3.0, then after 3 releases major.minor versions will be in sync with gitlab.

That would simplify the release process and potentially simplify it's automation.

E.g. we can create a manual CI job that will automatically:

  1. push a new release to pages
  2. create an MR targeting the appropriate branch in the gitlab repository

And then run it a few times a day.