Refactor ignition support during dracut

- Control root device using the node/profile root field
- Add support for `/warewulf/wwinit.d` to run scripts during first stage
- Move first-stage ignition support to `/warewulf/wwinit.d/`
- Add `wwctl <node|profile> set --parttype`
- Add overlay template functions `SystemdEscape` and `SystemdEscapePath`
- Support configuring ignition with resources

Signed-off-by: Jonathon Anderson <janderson@ciq.com>

userdocs/overlays/overlays.rst

@@ -192,8 +192,15 @@ In particular:
 - Update PAM configuration to allow missing shadow entries
 - Relabel the file system for SELinux
 
-Other overlays may place additional scripts in ``/warewulf/init.d/`` to affect
-node configuration in this pre-boot environment.
+Other overlays can place scripts in one of two locations for additional pre-init
+provisioning actions:
+
+- **/warewulf/wwinit.d/:** executed in the initial root final system before the
+  image is loaded into its final location. In a two-stage boot, these scripts
+  are executed in the Dracut initramfs.
+
+- **/warewulf/init.d/:** executed in the final root file system but before
+  calling ``init``.
 
 wwclient
 --------
@@ -309,6 +316,36 @@ ignition
 --------
 
 The **ignition** overlay defines partitions and file systems on local disks.
+Configuration may be provided via native disk, partition, and filesystem fields
+or via an ``ignition`` resource.
+
+.. code-block:: yaml
+
+   ignition:
+     storage:
+       disks:
+         - device: /dev/vda
+           partitions:
+             - label: scratch
+               shouldExist: true
+               wipePartitionEntry: true
+           wipeTable: true
+       filesystems:
+         - device: /dev/disk/by-partlabel/scratch
+           format: btrfs
+           path: /scratch
+           wipeFilesystem: false
+
+If any disk/partition/filesystem configuration is provided for a node with
+explicit arguments to ``wwctl <node|profile> set``, the ``ignition`` resource is
+ignored.
+
+To use ignition during Dracut (so that the root file system may be provisioned
+before the image is loaded) include Ignition in the Dracut image.
+
+.. code-block:: shell
+
+   wwctl image exec rockylinux-9 -- /usr/bin/dracut --force --no-hostonly --add wwinit --add ignition --regenerate-all
 
 debug
 -----

userdocs/overlays/templates.rst

@@ -148,7 +148,13 @@ symlink.
 IgnitionJson
 ------------
 
-Generates JSON suitable for use by Ignition to create 
+Generates JSON suitable for use by Ignition to create partitions and file
+systems, from the data stored in a node's native ``disks`` and ``filesystems``
+fields.
+
+.. code-block::
+
+   {{ IgnitionJson }}
 
 abort
 -----
@@ -174,10 +180,9 @@ nobackup
 UniqueField
 -----------
 
-UniqueField returns a filtered version of a multi-line input string. input is
-expected to be a field-separated format with one record per line (terminated by
-`\n`). Order of lines is preserved, with the first matching line taking
-precedence.
+Returns a filtered version of a multi-line input string. input is expected to be
+a field-separated format with one record per line (terminated by `\n`). Order of
+lines is preserved, with the first matching line taking precedence.
 
 For example, the following template snippet has been used in the ``syncuser`` overlay
 to generate a combined ``/etc/passwd``.
@@ -191,6 +196,24 @@ to generate a combined ``/etc/passwd``.
        | UniqueField ":" 0 | trim
    }}
 
+SystemdEscape
+-------------
+
+Escapes a string for use in a systemd unit file.
+
+Escape rules are documented at `systemd.unit. <https://www.freedesktop.org/software/systemd/man/latest/systemd.unit.html#String%20Escaping%20for%20Inclusion%20in%20Unit%20Names>`_
+
+SystemdEscapePath
+-----------------
+
+Escapes a path for use in a systemd unit file.
+
+.. code-block::
+
+   {{ file (print ($fs.path | SystemdEscapePath) ".mount") }}
+
+Escape rules are documented at `systemd.unit. <https://www.freedesktop.org/software/systemd/man/latest/systemd.unit.html#String%20Escaping%20for%20Inclusion%20in%20Unit%20Names>`_
+
 Examples
 ========