CI: also build tier-0 and tier-x

Let's at least verify tier-0 and tier-x can build fine. Ideally in the
future we actually run some tests on the resulting image, though let's
wait until this CI is migrated to Konflux before doing that.

.gitlab-ci.yml

@@ -4,8 +4,11 @@ include:
 
 build-image:
   extends: .build-image
+  parallel:
+    matrix:
+      - TIER: [tier-0, tier-1, tier-x]
   variables:
-    EXTRA_ARGS: "--security-opt=label=disable --cap-add=all"
+    EXTRA_ARGS: "--security-opt=label=disable --cap-add=all --build-arg MANIFEST=fedora-$TIER.yaml"
   rules:
     - if: $CI_PROJECT_NAMESPACE != "fedora/bootc"
       when: never

fedora-tier-1.yaml

@@ -0,0 +1 @@
+fedora-bootc.yaml