Merge branch '421414-cells-iteration-2-convert-fk-between-users-notification_settings' into 'master' 

Convert notification_settings.user_id to loose foreign key

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/130080



Merged-by: Prabakaran Murugesan <pmurugesan@gitlab.com>
Approved-by: Rutger Wessels <rwessels@gitlab.com>
Approved-by: Mohamed Hamda <mhamda@gitlab.com>
Approved-by: Prabakaran Murugesan <pmurugesan@gitlab.com>
Approved-by: Ahmed Hemdan <ahemdan@gitlab.com>
Reviewed-by: Ahmed Hemdan <ahemdan@gitlab.com>
Reviewed-by: Mohamed Hamda <mhamda@gitlab.com>
Reviewed-by: Rutger Wessels <rwessels@gitlab.com>
Reviewed-by: Prabakaran Murugesan <pmurugesan@gitlab.com>
Co-authored-by: Manoj M J <mmj@gitlab.com>