Upgrade webpack and webpack-dev-server to latest

What does this MR do?

• Fixes issue with breakpoints being off by a couple lines due to bad sourcemaps (closes #30588 (closed))
  https://github.com/webpack/webpack/releases/tag/v2.3.2
• Fixes websockets issue with Firefox causing strange reloading behavior (closes #28438 (closed))
  https://github.com/webpack/webpack-dev-server/issues/762
• Fixes issue in which webpack-dev-server wouldn't terminate properly in docker (see gitlab-development-kit!252 (closed), gitlab-development-kit!253 (merged)) https://github.com/webpack/webpack-dev-server/pull/787

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

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [ ] 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?

Closes #30588 (closed)