feat: add resolve_paths_from_workdir option for relative path resolution

[deadbaed]

Closes #1049

Adds new flag resolve_paths_from_workdir, available on the CLI, Trunk.toml, and the RESOLVE_PATHS_FROM_WORKDIR environment variable.

I followed the instructions in the contributing.md file, I hope I did not forget anything.

[deadbaed]

This works for trunk build, but when using trunk serve on an index.html file inside /nix/store/ it causes a delay of ~2 mins before the webserver launches.

When investigating it is because build_watcher() has to look over all the files in that directory, which is big.