Enable gating based on BaseOS CI results

Based on [1], enables gating governed by BaseOS CI results.

[1] https://docs.google.com/document/d/1zvG03jABz8Od6W8YkQ8ewOKt10kzmQ0KYNjL1QOcKoE/

gating.yaml

@@ -0,0 +1,6 @@
+--- !Policy
+product_versions:
+  - rhel-8
+decision_context: osci_compose_gate
+rules:
+  - !PassingTestCaseRule {test_case_name: baseos-ci.brew-build.tier1-gating.functional}