Adding persistent paths after install

Drop a file under /oem/91_paths.yaml with the following content:

stages:
  rootfs:
    - name: "Custom mounts"
      environment_file: /run/cos/cos-layout.env
      environment:
        CUSTOM_BIND_MOUNTS: "/var/lib/path1 /var/lib/path2 /var/lib/path3"

This will indicate to Kairos to bind mount the paths /var/lib/path1, /var/lib/path2, and /var/lib/path3 to the persistent partition under /usr/local/.state after the next reboot.