Docker use node 16 and udev, generic debian base.

[easytarget]

This updates the Dockerfile to support recent serialport changes and improve cross-platform support.

Changed the base image to the 'official' node16/bullseye image; this brings support for multiple platforms (armhf, arm64, i32, x64, ppc), and better supports node serialport + udev.

Added a DOCKER.md document to the repo detailing how to build+run with the correct nice setting.

[cprezzi]

@easytarget Do you want me to merge this PR? You should be able to merge it yourself.

[easytarget]

@cprezzi It's not urgent, and I did want your feedback since I dont want to break anything that may rely on the docker build. I'm a bit concerned about if it is being used in the electron build.

Also; I dont seem to be able to merge this; not sure what is up there but I see 'Only those with write access to this repository can merge pull requests.` above; so I assume something went wrong there..

[cprezzi]

I saw that you never acepted my invitation to the LaserWeb devteam. Now I re-invited you to the LaserWeb devteam and core-devs. You need to accept the invitation ;)

[easytarget]

Ok, I've got it now. I obviously missed the mail first time around. Thanks!

[cprezzi]

@easytarget Do you want to finaly merge this PR? The docker file is not used for the electron build.