Merge branch 'ms-limit-issue-email-participants' into 'master'

Limit external participants on a single issue

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/138812



Merged-by: Stan Hu <stanhu@gmail.com>
Approved-by: Marcos Rocha <mrocha@gitlab.com>
Approved-by: Stan Hu <stanhu@gmail.com>
Reviewed-by: Marc Saleiko <msaleiko@gitlab.com>
Co-authored-by: Marc Saleiko <msaleiko@gitlab.com>