Define tier0 testing

As part of tier0 unification across the rhel-pt-gcc components
(RHEL-113756), introduce tier0 testing. The testing is limited
to x86_64-only (OSCI-imposed).

The tests selected for it are the public part of tier1. In other
words, we are introducing tier0 as a subset of tier1, run on
x86_64-only.

For awareness, RHEL builds get full tier1 in a later phase of
gating (BaseOS CI). This commit doesn't affect that in any way;
now we are just adding a small bit of functional testing sooner
in the pipeline.

.fmf/version

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

plans/ci.fmf

@@ -1,5 +0,0 @@
-summary: CI Gating Plan
-discover:
-    how: fmf
-execute:
-    how: tmt

plans/tier0.fmf

@@ -0,0 +1,34 @@
+# Tier 0 test plan. It's actually Tier 1
+#   - limited to its public part
+#   - executed on the architecture at hand
+# When run by osci.tier0 on CentOS Stream or RHEL, it receives the following
+# context:
+#   arch=x86_64 (the architecture at hand, currently OSCI uses just x86_64)
+#   distro=rhel<M>.<m> (even for CentOS Stream builds)
+#   trigger=build
+
+summary: Tier 0 test plan
+context:
+  collection: gcc-toolset-14
+environment+:
+  COLLECTIONS: gcc-toolset-14
+  WITH_SCL: "scl enable gcc-toolset-14"
+discover:
+  - name: collect_info
+    how: shell
+    tests:
+      - name: /info/rpms
+        test: rpm -qa --last
+  - name: public_tests
+    how: fmf
+    url: https://gitlab.com/redhat/centos-stream/tests/annobin.git
+    filter: tier:1
+prepare:
+  - how: shell
+    script:
+      - dnf config-manager --set-enabled '*CRB*' || true
+      - dnf config-manager --set-enabled crb || true
+      - dnf config-manager --set-enabled rhel-buildroot || true
+      - dnf config-manager --set-enabled '*debuginfo*' || true
+execute:
+  how: tmt