tier-0: Rename to minimal

The "tiers" nomenclature ended up being unhelpful since
we introduced "tier-x" which is between tier-0 and tier-1.

We also never exposed the tier naming outside of our source
code. In preparation for doing so, rename to tier-0 to
"minimal" which is a bit more descriptive.

Renaming the other images will follow.

Signed-off-by: Colin Walters <walters@verbum.org>

minimal/tmpfiles.yaml

@@ -0,0 +1,7 @@
+postprocess:
+  - |
+    #!/bin/bash
+    cat >/usr/lib/tmpfiles.d/bootc-base-rpmstate.conf <<'EOF'
+    # Workaround for https://bugzilla.redhat.com/show_bug.cgi?id=771713
+    d /var/lib/rpm-state 0755 - - -
+    EOF