Set 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 the public part 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; we are
adding a small bit of functional testing sooner in the pipeline.

.fmf/version

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+1

plans/tier0.fmf

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+# 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
+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