Bootable Containers: Enable composefs by default

Only enabled for bootable containers as we need to remove ostree-grub2
first.

See: https://fedoraproject.org/wiki/Changes/ComposefsAtomicCoreOSIoT

common-bootable-containers-kinoite.yaml

@@ -13,3 +13,4 @@ packages:
 include:
   # - dnf5-bootc.yaml
   - bootupd.yaml
+  - composefs.yaml

common-bootable-containers.yaml

@@ -2,3 +2,4 @@
 include:
   - dnf5-bootc.yaml
   - bootupd.yaml
+  - composefs.yaml

composefs.yaml

@@ -0,0 +1,11 @@
+# Set up composefs by default
+# See: https://fedoraproject.org/wiki/Changes/ComposefsAtomicCoreOSIoT
+postprocess:
+  - |
+    #!/usr/bin/env bash
+    set -xeuo pipefail
+
+    cat >> /usr/lib/ostree/prepare-root.conf << 'EOF'
+    [composefs]
+    enabled = yes
+    EOF