Merge branch 'mmj-doc-changes-16' into 'master'

Documentation update for breaking changes in 16.0

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/119601



Merged-by: Lorena Ciutacu <lciutacu@gitlab.com>
Approved-by: Lorena Ciutacu <lciutacu@gitlab.com>
Reviewed-by: Manoj M J <mmj@gitlab.com>
Reviewed-by: Lorena Ciutacu <lciutacu@gitlab.com>
Co-authored-by: Manoj M J <mmj@gitlab.com>