`snapcraft clean <part> --use-lxd` shouldn't wait for network

[Omer Akram]

When cleaning a specific part, please make it so, so that snapd doesn't wait for the availability of internet, it's redundant to wait for network connectivity for the lxd container, while the sole purpose is to just delete a few directories.

This will help developers who are debugging their code and need to clean specific part frequently. All saved seconds are helpful.

[Sergio Schvezov (sergiusens)]

https://github.com/snapcore/snapcraft/blob/main/snapcraft/internal/build_providers/_lxd/_lxd.py#L406 is where this is at. I believe we have this to avoid slow network bringups.

--offline could be passed together with clean.
We need to analyze and see if we can do without waiting for network all-together.