Add support for Jest config

[felixjb]

Describe the solution you'd like
Add support for jest.config.js or jest field in package.json

Additional context
This issue was first opened at the original repo.

[roggenbrot]

I think one solution could be using jest command line to print jest config as json (https://jestjs.io/docs/en/cli#showconfig) and the parse the output.

What I don't know if this is causing any performance problems. Also detecting the path to jest could be a problem (See existing issues for windows, gitcmd .....)

[felixjb]

@roggenbrot you're here! 🎉 Thank you for contributing!

I'll look into it! Thank you!