Add scan result policy access check

Why we are doing this work

• We want to stop people from pushing and force-pushing to branches that are affected by scan result policies, even if they have enabled the "Allowed to force push" option of a protected branch:

Implementation Plan

A PoC is available on the 420629-add-scan-result-policy-access-check branch.

• backend Add a feature flag

• backend Change the error message to:

  Force push is blocked by settings overridden by security policies:
  * {policy-name and link}

• backend prevent pushing and force pushing