Relocate HAOS Systemd drop-ins to /usr/lib/systemd (#3582)

* Relocate HAOS Systemd drop-ins to /usr/lib/systemd

With some exceptions, Systemd drop-ins overriding default unit configuration
have been placed to `/etc/systemd/system`. This is meant for user overrides of
those, or per `man 5 systemd.unit` for "system unites created by the
administrator". Relocate all of these to `/usr/lib/systemd` which should be
used as path for units "installed by the distribution package manager" which is
closer to what we're trying to achieve.

This will make it easier to detect changes to unit files once we enable the
possibility to edit the content of /etc.

* Patch systemd-timesyncd.service instead of replacing it fully

buildroot-external/rootfs-overlay/usr/lib/systemd/system/docker.service.d/failure.conf

@@ -0,0 +1,6 @@
+[Unit]
+FailureAction=reboot
+
+[Service]
+ExecStartPre=/usr/libexec/docker-disk-check
+ExecStopPost=/usr/libexec/docker-failure

buildroot-external/rootfs-overlay/usr/lib/systemd/system/docker.service.d/hassos.conf

@@ -0,0 +1,5 @@
+[Unit]
+RequiresMountsFor=/etc/docker /mnt/data /var/lib/docker
+
+[Service]
+OOMScoreAdjust=-400

buildroot-external/rootfs-overlay/usr/lib/systemd/system/docker.service.d/resource.conf

@@ -0,0 +1,2 @@
+[Service]
+TasksMax=infinity