Merge branch 'mdangelo/update_quick_actions_md_with_set_parent_epic_alias' into 'master'

Update docs to include /set_parent on legacy issues

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/183603



Merged-by: Marcin Sedlak-Jakubowski <msedlakjakubowski@gitlab.com>
Approved-by: Marcin Sedlak-Jakubowski <msedlakjakubowski@gitlab.com>
Co-authored-by: Matt D'Angelo <mdangelo@gitlab.com>