Added approver notification setting

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/137006



Merged-by: Kerri Miller <kerrizor@kerrizor.com>
Approved-by: Juliet Wanjohi <jwanjohi@gitlab.com>
Approved-by: Max Orefice <morefice@gitlab.com>
Approved-by: Alper Akgun <aakgun@gitlab.com>
Approved-by: Kerri Miller <kerrizor@kerrizor.com>
Reviewed-by: Gabriel Mazetto <brodock@gmail.com>
Reviewed-by: Max Orefice <morefice@gitlab.com>
Reviewed-by: Juliet Wanjohi <jwanjohi@gitlab.com>
Co-authored-by: Phil Hughes <me@iamphill.com>