tier-0: explicitly list coreutils

This currently is already in tier-0, but it feels odd to not explicitly
list it. Noticed while comparing to FCOS manifests, which does list it.

tier-0/manifest.yaml

@@ -53,6 +53,8 @@ include:
   - basic-fixes.yaml
 
 packages:
+  # this is implied by dependencies but let's make it explicit
+  - coreutils
   # needed for building derived container images
   - dnf5
   # Even in tier-0, we have this.  If you don't want SELinux today, you'll need