Merge branch 'axil-docs-major-version-removal-guideline' into 'master'

Add docs guideline when to remove mentions of old versions

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/150748



Merged-by: Suzanne Selhorn <sselhorn@gitlab.com>
Reviewed-by: Achilleas Pipinellis <axil@gitlab.com>
Reviewed-by: Evan Read <eread@gitlab.com>
Co-authored-by: Achilleas Pipinellis <axil@gitlab.com>