Merge branch 'add_backend_for_participants_widget' into 'master'

Add participants widget

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/141097



Merged-by: Leonardo da Rosa <ldarosa@gitlab.com>
Approved-by: Ross Byrne <robyrne@gitlab.com>
Approved-by: Leonardo da Rosa <ldarosa@gitlab.com>
Reviewed-by: Luke Duncalfe <lduncalfe@gitlab.com>
Reviewed-by: Alexandru Croitor <acroitor@gitlab.com>
Reviewed-by: charlie ablett <cablett@gitlab.com>
Reviewed-by: Leonardo da Rosa <ldarosa@gitlab.com>
Co-authored-by: Alexandru Croitor <acroitor@gitlab.com>