Merge branch 'notifications-todos-mobile-issue' into 'master'

Remove notifications from sm issue dropdown behind feature flag

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/138374



Merged-by: Phil Hughes <me@iamphill.com>
Approved-by: Phil Hughes <me@iamphill.com>
Approved-by: Sascha Eggenberger <seggenberger@gitlab.com>
Co-authored-by: Annabel Dunstone Gray <annabel.dunstone@gmail.com>