feat: allows setting a working dir

[cristianoliveira]

This is a need that I feel everytime I need to work with monorepos, sometimes adapting the scripts to run from the root folder takes longer than just running funzzy inside of each project

 - name: setup install
  workdir: ./myapp/ # This would be similar to `cd ./myapp/ && npm install`
  run: npm install
  run_on_init: true
  change: package.json

[cristianoliveira]

NOTE: Check how we change dir before running fzz in the tests, maybe that's the way to go

funzzy/tests/command_init.rs

Line 9 in 9844b75

std::env::set_current_dir("examples/workdir/ignored").expect("failed to change dir");