Plain mode: support port forwarding (opt-in)

[AkihiroSuda]

limactl create --plain is useful to disable Lima's opinionated extensions, but it still makes sense to allow port forwarding as an opt-in feature.

In the case of plain mode, the port list should be obtained from the explicit list in YAML/CLI, not from the guest agent (which shouldn't be running at all in the case of plain mode).

Workaround

The current workaround is to run ssh -L manually:

ssh -q -f -N -L 6443:127.0.0.1:6443 -F ~/.lima/host0/ssh.config lima-host0

[Ranjandas]

On the same note, it would be great if the environment variables (/mnt/lima-cidata/etc_environment)were also fed to the scripts that are run with provision.mode: user. Currently, in plain mode, looks like the user script don't see these variables and we are forced to run everything with provision.mode: system