Merge branch 'add-severity-override-to-instance-level' into 'master'

Add severity override to instance level

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/183674



Merged-by: Michael Becker <mbecker@gitlab.com>
Approved-by: Lorenz van Herwaarden <lvanherwaarden@gitlab.com>
Approved-by: Michael Becker <mbecker@gitlab.com>
Reviewed-by: Michael Becker <mbecker@gitlab.com>
Co-authored-by: Chen Charnolevsky <ccharnolevsky@gitlab.com>