Make MR not mergeable if License Compliance has found denied licenses

This is a part of #196845 (closed)

If MR has successfully finished license_scanning job and some denied licenses are found, we need to prevent merging of Merge Request.

Implementation plan

1. Hide all work behind feature flag license_compliance_denies_mr
2. Define if MR has denied licenses (SoftwareLicensePoliciesFinder and LicenseScanningReportLicenseEntity for the reference)
3. Add a field policy_violation (true/false) to EE::MergeRequestPollCachedWidgetEntity with value found on previous step.
4. Change MergeRequest object state to not mergeable if denied licenses are found. Keep in mind that this is EE feature and work should be done in ee directory. This step can be dangerous so it requires thorough testing.