Enable gating via tmt plans in testing farm.

There's an extesion of testing with this commit. Where previously we
were running CI-Tier-1 tests for librepo + ci-dnf-stack, now we will
run CI-Tier-1 tests for dnf + librepo + ci-dnf-stack.

.fmf/version

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

ci.fmf

@@ -0,0 +1 @@
+resultsdb-testcase: separate

gating.yaml

@@ -5,3 +5,4 @@ decision_context: osci_compose_gate
 rules:
   - !PassingTestCaseRule {test_case_name: baseos-ci.brew-build.tier1-gating.functional}
   - !PassingTestCaseRule {test_case_name: baseos-ci.brew-build.ci-dnf-stack-gating.functional}
+  - !PassingTestCaseRule {test_case_name: osci.brew-build./plans/internal/CI-Tier-1.functional}

plans/internal/CI-Tier-1.fmf

@@ -0,0 +1,15 @@
+summary: Internal CI-Tier-1 tests plan
+discover:
+  - name: librepo
+    how: fmf
+    filter: 'tag: CI-Tier-1'
+    url: https://pkgs.devel.redhat.com/git/tests/librepo
+  - name: dnf
+    how: fmf
+    filter: 'tag: CI-Tier-1'
+    url: https://pkgs.devel.redhat.com/git/tests/dnf
+execute:
+    how: tmt
+adjust:
+    enabled: false
+    when: distro == centos-stream or distro == fedora