deploy: add pre-deploy actions to TOML

The idea is provide a way for the user to run a command

```
[[tool.robotpy.deploy]]
command = ["python", "-m", "mypy"]
required = False # if false won't stop the deploy if it fails

```

Allows users to do https://github.com/robotpy/pyfrc/issues/206 if they want.

Arguably, this really isn't necessary -- users can already implement whatever they want by adding a 'deploy.sh' shell script and making everyone use that, but maybe this is better?