Automate blocking of MR if new vulnerabilites detected

https://docs.gitlab.com/ee/development/code_review.html#the-responsibility-of-the-maintainer asks maintainers to:

must check before merging if the merge request is introducing new vulnerabilities, by inspecting the list in the merge request Security Widget.

Could we automate this by using https://docs.gitlab.com/ee/user/application_security/policies/scan-result-policies.html ?

/cc @gitlab-com/gl-security/appsec