Merge branch 'ui-doc-link-md-extension-1' into 'master'

Update HAML help page links to use .md extension - 1

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/164834



Merged-by: Peter Leitzen <pleitzen@gitlab.com>
Approved-by: Peter Leitzen <pleitzen@gitlab.com>
Approved-by: Smriti Garg <sgarg@gitlab.com>
Reviewed-by: Peter Leitzen <pleitzen@gitlab.com>
Co-authored-by: Marcel Amirault <mamirault@gitlab.com>