Script to update Pages version on GitLab repo

What does this MR do?

I've been basically doing these steps manually every month (example), so I though would be nice to script-ize these for future reference and consistency.

❓ Alternatively, I thought in maybe automatize this in a cron task on our CI to always create this MR on GitLab, to ensure we have GitLab pages updated on the main repository at least once a month. Not sure how to do that, though.

---

This script, to be used in the developer machine, creates a commit with the list of changes (commit titles) between the current version of pages in gitlab/GITLAB_PAGES_VERSION and GitLab Pages master. That commit is done in update-gitlab-pages-version branch, which is then pushed creating a MR with all the required labels on GitLab.

The commit message follow the template:

Update gitlab-pages

Main changes:
* Commit 1 title
* Commit 2 title
* Commit 3 title
* Commit 4 title

Reference: https://gitlab.com/gitlab-org/gitlab-pages/-/compare/CURRENT_COMMIT...master

Changelog: changed

TODO

• Feature flag
  • Added feature flag:
  • This feature does not require a feature flag
• I added the Changelog trailer to the commits that need to be included in the changelog (e.g. Changelog: added)
• I added unit tests or they are not required
• I added acceptance tests or they are not required
• I added documentation (or it's not required)
• I followed code review guidelines
• I followed Go Style guidelines