Migrate to TMT-style gating in C9S

This is required for RHIVOS, see VROOM-23635.

.fmf/version

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

gating.yaml

@@ -3,4 +3,4 @@ product_versions:
   - rhel-9
 decision_context: osci_compose_gate
 rules:
-  - !PassingTestCaseRule {test_case_name: baseos-ci.brew-build.tier1.functional}
+  - !PassingTestCaseRule {test_case_name: osci.brew-build.tier0.functional}

plans/tier1.fmf

@@ -0,0 +1,39 @@
+---
+
+summary: Tier1 plan for libuser
+
+discover:
+  how: fmf
+  url: https://pkgs.devel.redhat.com/git/tests/libuser
+  ref: master
+  filter: tier:1
+
+prepare:
+  - how: shell
+    script: |
+      set -euxo pipefail
+
+      ENABLE_REPO_CMD="yum-config-manager --enable"
+      if command -v dnf >/dev/null 2>&1; then
+        ENABLE_REPO_CMD="dnf config-manager --set-enabled"
+      fi
+
+      ${ENABLE_REPO_CMD} beaker-tasks || :
+  - how: shell
+    script: |
+        set -exuo pipefail
+
+        if [[ -f /etc/os-release ]]; then
+          . /etc/os-release
+          if [[ "${ID:-}" == "rhel" && "${VERSION_ID%%.*}" -ge 8 ]]; then
+            dnf config-manager --enable rhel-CRB
+          fi
+        fi
+
+execute:
+  how: tmt
+
+adjust:
+    enabled: false
+    when: distro == centos-stream or distro == fedora
+