feat: add --persist so SNO VM survives the host reboot

[xiormeesh]

When using miniagent/SNO instead of Openshift Local/crc sometimes the host needs to be rebooted without losing the SNO VM, this PR

• adds --persist flag defaulting to false
• enables autostart for both network and VM
• unmounts installation ISO file from the VM since it's stored in /tmp and would not survive a reboot
• copies /tmp/mini-agent/auth/kubeconfig to /var/lib/miniagent/kubeconfig (overwrites if exists but should not be an issue since miniagent supports only one SNO VM at a time anyway)

I've decided to gate the functionality behind --persist flag because based on our previous conversations most users need miniagent for quick tests and I wanted to keep the ephemeral usecase as is.