Announce AmazonLinux 2 deprecation

AmazonLinux 2 (AL2) is scheduled to go EOL on 2025-06-30. With #8844 (closed) all users should be unblocked to upgrade to AL 2023.

We can now deprecate AL2 and remove it after 2025-06-30.

Update: AL2 EOL was extended for another year.

Update the Omnibus deprecations list: https://gitlab.com/gitlab-org/omnibus-gitlab/-/blob/be06635ddffca966609f590a277bec5431525153/files/gitlab-cookbooks/package/libraries/omnibus_helper.rb#L170
Announce the deprecation. Last time we did this was in gitlab!169713 (merged).
Create a follow-up to remove CI jobs, builders, and our supported OS documentation.

Edited Jan 22, 2025 by Clemens Beck