Support Dotenv

[glennreyes]

Similar to CRA, I've found it useful to have that supported out of the box.

[manpenaloza]

would like to deal with that if ok (?).

just some questions upfront:

• what's the main goal of this to be considered when implementing (especially regarding a cleaner code base)?
• is it ok to use oss packages like https://github.com/motdotla/dotenv to solve this?

[glennreyes]

I'd propose https://webpack.js.org/plugins/environment-plugin/#dotenvplugin. Ideally .env works well together with webpack.Environmentplugin (when set in the graphpack.config.js)