only print errors and warnings from webpack dev server

What does this MR do?

reduce noisy output from webpack with build about. Still prints warnings and errors.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Output is not useful for common case

Screenshots (if relevant)

New output:

13:15:08 webpack.1               | 
13:15:08 webpack.1               | WARNING in ./vendor/assets/javascripts/es6-promise.auto.js
13:15:08 webpack.1               | Module not found: Error: Can't resolve 'vertx' in 'src/gitlab-development-kit/gitlab/vendor/assets/javascripts'
13:15:08 webpack.1               |  @ ./vendor/assets/javascripts/es6-promise.auto.js 140:16-26
13:15:08 webpack.1               |  @ ./app/assets/javascripts/application.js
13:15:08 webpack.1               |  @ multi (webpack)-dev-server/client?http://localhost:3808 ./application.js
13:15:08 webpack.1               | webpack: Compiled with warnings.

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

#27881 (closed)

/cc @rspeicher