List latest 3 stable versions in the version check endpoint

Problem

In #344682 (closed) we are looking to include more information to admins to encourage upgrading for critical security updates.

One of the items we would like to see is:

A list of suggested versions will need to be provided by the Version Check API so that the instance knows which versions to suggest

Proposal

Include the lastest patch release of the last 3 feature releases in https://gitlab.com/gitlab-services/version-gitlab-com/-/blob/master/app/controllers/version_checks_controller.rb

Potentially exclude versions that are less/equal to the version information in the gitlab info.

NOTE: From discussion with the requesting party:

>Would it be enough to show Version.last(3)

No, I think it needs to be smarter, as if we do a critical security release, or a far-back backport (rare but happens), we don't want it returning those old patches.
From the latest 3 stable versions we expect them to be:

Each be a different feature release, latest 3 feature releases as determined via semver (not via release date)
Return only the latest semver path from those feature release.

So it's a bit complicated. The release-tools repo has some version files that have to do some similar work that might help as reference: https://gitlab.com/gitlab-org/release-tools/-/blob/master/lib/release_tools/version.rb and https://gitlab.com/gitlab-org/release-tools/-/blob/master/lib/release_tools/versions.rb

Result

GitLab UI is able to present more than just the latest version as a viable update target for critical security releases.