enhancement: support for rke2 embedded-registry feature

[jgnoguer]

Currently we cannot benefit from the k3s/rke2 embedded-registry feature when deploying an RKE2 node with Rancher in an Air-Gap environment.

https://docs.rke2.io/install/registry_mirror

It would be great if rancher-system-agent was able to use the embedded-registry-mirror as for the rke2-agent.