Merge branch 'sf/chore/add-instance-saml-spec' into 'master'

Spec approval service for instance SAML approval

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/142349



Merged-by: Dmitry Gruzd <dgruzd@gitlab.com>
Approved-by: Jonas Larsen <jlarsen@gitlab.com>
Approved-by: Dmitry Gruzd <dgruzd@gitlab.com>
Co-authored-by: Sam Figueroa <sfigueroa@gitlab.com>