add css extraction and minification to webpack (#9944)

This changes the CSS output of webpack to output to the public/css
directory instead of inling CSS in JS. This enables CSS minification and
autoprefixer based on browserslist which would otherwise not be
possible.

The result of this change is two new output files currently:

- public/css/swagger.css
- public/css/gitgraph.css

Co-authored-by: techknowlogick <[email protected]>

Author: 2 people