Add DefinePlugin to webpack configuration

[Crashillo]

Currently is enabled in some other modules. But yes, it's not a good practice, the ideal is about to have something like this: https://webpack.js.org/plugins/environment-plugin/, then just replace that true with process.env.DEBUG

Originally posted by @Crashillo in #3663 (comment)

Once done, replace Vue.config.devtools (perhaps some other stuff) with the properly value