Bring gating.yaml over from Brew dist-git

Signed-off-by: Troy Dawson <tdawson@redhat.com>

gating.yaml

@@ -0,0 +1,9 @@
+--- !Policy
+product_versions:
+  - rhel-8
+decision_context: osci_compose_gate
+rules:
+  # istack-commons is a build dependency of glassfish-jaxb.
+  # The manual gating should ensure that glassfish-jaxb builds
+  # successfully with any updates to istack-commons
+  - !PassingTestCaseRule {test_case_name: manual.sst_identity_management.istack-commons.glassfish-jaxb-builds}