Enable gating tests

Add a gating.yaml to make sure that newer Cockpit versions don't enter
stable when they cause regressions in various static RPM checks or our
CI tests.

See https://docs.pagure.org/greenwave/policies.html

gating.yaml

@@ -0,0 +1,11 @@
+--- !Policy
+product_versions:
+  - fedora-33
+  - fedora-rawhide
+decision_context: bodhi_update_push_stable
+rules:
+  - !PassingTestCaseRule {test_case_name: dist.rpmgrill.security-policy}
+  - !PassingTestCaseRule {test_case_name: dist.rpmgrill.spec-file-sanity}
+  - !PassingTestCaseRule {test_case_name: dist.python-versions}
+  - !PassingTestCaseRule {test_case_name: dist.abicheck}
+  - !PassingTestCaseRule {test_case_name: fedora-ci.koji-build.tier0.functional}