Improve hauler usage after first boot

[e-minguez]

After the first boot has been completed, hauler is still there serving images. It also performs the load operation even if the images are there:

vm1:~ # systemctl cat eib-embedded-registry.service
# /etc/systemd/system/eib-embedded-registry.service
[Unit]
Description=Load and Serve Embedded Registry
After=network.target

[Service]
Type=simple
User=root
WorkingDirectory=/opt/hauler
ExecStartPre=/bin/sh -c '/opt/hauler/hauler store load *-registry.tar.zst'
ExecStart=/opt/hauler/hauler store serve registry -p 6545
Restart=on-failure

[Install]
WantedBy=multi-user.target

NOTE: The store load operation probably won't affect too much if hauler recognizes the images and don't load them if they are there. I'm not sure if it does.

Also, it seems every image is stored 3 times per host:

• the zst file
• the image being served in the local registry
• the image on the local container cache

vm1:/opt/hauler # ls -lh registry.rancher.com_rancher_rancher\:v2.9.1-registry.tar.zst
-rw-r--r--. 1 root root 750M Nov 19 16:14 registry.rancher.com_rancher_rancher:v2.9.1-registry.tar.zst
|
vm1:/opt/hauler # ./hauler store info | grep -i rancher/rancher
| rancher/rancher:v2.9.1                        | image | linux/arm64 |       25 | 790.8 MB |

vm1:/opt/hauler # /var/lib/rancher/rke2/bin/crictl images | grep rancher/rancher
registry.rancher.com/rancher/rancher-webhook                         v0.5.1                                             52ce404b3faf3       26.3MB
registry.rancher.com/rancher/rancher                                 v2.9.1                                             0bb0d5da44771       791MB