tier-0: add kernel-install integration config

This MR adds two configurations to enable kernel-install integration,
this will enable using dnf or rpm to install kernels.

- /usr/lib/kernel/install.conf: enables the hook that tells kernel-install
to defer the logic to rpm-ostree, this currently only on f42
- dnf.conf: ensures dnf only keeps one kernel package

tier-0/kernel-install.yaml

@@ -0,0 +1,24 @@
+# Configuration to enable kernel-install integration
+postprocess:
+  - |
+    #!/usr/bin/env bash
+    set -xeuo pipefail
+    source /usr/lib/os-release
+    # Check if the ID is Fedora and VERSION_ID is 42 or higher
+    if [[ "$ID" == "fedora" && "$VERSION_ID" -ge 42 ]]; then
+        echo -e "# kernel-install will not try to run dracut and allow rpm-ostree to\n\
+    # take over. Rpm-ostree will use this to know that it is responsible\n\
+    # to run dracut and ensure that there is only one kernel in the image\n\
+    layout=ostree" | tee /usr/lib/kernel/install.conf > /dev/null
+    fi
+    # By default dnf keeps multiple versions of the kernel, with this
+    # configuration we tell dnf to treat the kernel as everything else.
+    # https://dnf.readthedocs.io/en/latest/conf_ref.html#main-options
+    # Let's add the config to a distribution configuration file if dnf5
+    # is used, we append to /etc/dnf/dnf.conf if not.
+    if [ -d "/usr/share/dnf5/libdnf.conf.d/" ]; then
+      echo -e "[main]\ninstallonlypkgs=''" >> /usr/share/dnf5/libdnf.conf.d/20-ostree-installonlypkgs.conf
+    else
+      echo "installonlypkgs=''" >> /etc/dnf/dnf.conf
+    fi
+

tier-0/manifest.yaml

@@ -21,6 +21,7 @@ include:
   - ostree.yaml
   - initramfs.yaml
   - basic-fixes.yaml
+  - kernel-install.yaml
 
 packages:
   # this is implied by dependencies but let's make it explicit