Add test plan to run butane gating tests

Ref: https://issues.redhat.com/browse/COS-2283

.fmf/version

@@ -0,0 +1 @@
+1

gating.yaml

@@ -3,4 +3,4 @@ product_versions:
   - rhel-10
 decision_context: osci_compose_gate
 rules:
-  - !PassingTestCaseRule {test_case_name: osci.brew-build.tier0.functional}   # this is the testcase identifier, which OSCI pipeline uses
+  - !PassingTestCaseRule {test_case_name: osci.brew-build./plans/smoke}   # this is the testcase identifier, which OSCI pipeline uses

plans/smoke.fmf

@@ -0,0 +1,8 @@
+summary: Run gating tests 
+discover:
+    - name: Internal gating tests
+      how: fmf
+      url: https://github.com/coreos/butane.git
+      filter: 'tag: smoke'
+execute:
+    how: tmt