Merge branch '451784-be-support-fallback_behavior-for-approval-policies' into 'master'

Support `fallback_behavior` for MR approval policies

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/147838



Merged-by: Sashi Kumar Kumaresan <skumar@gitlab.com>
Approved-by: Martin Čavoj <mcavoj@gitlab.com>
Approved-by: Sashi Kumar Kumaresan <skumar@gitlab.com>
Approved-by: Jon Jenkins <jjenkins@gitlab.com>
Reviewed-by: Terri Chu <tchu@gitlab.com>
Reviewed-by: Sashi Kumar Kumaresan <skumar@gitlab.com>
Reviewed-by: Martin Čavoj <mcavoj@gitlab.com>
Co-authored-by: Dominic Bauer <dbauer@gitlab.com>
Co-authored-by: Martin Čavoj <mcavoj@gitlab.com>
Co-authored-by: Russell Dickenson <rdickenson@gitlab.com>