Fix: serve generated assets

[developit]

When karma-webpack was switched to generating files on disk, only commons.js and runtime.js were configured to be served. This serves the rest of the contents of the output directory.

This PR contains a:

• [x] bugfix
• [ ] new feature
• [ ] code refactor
• [ ] test update
• [ ] typo fix
• [ ] metadata update

Motivation / Use-Case

I am attempting to update from karma-webpack@4, but bundles/assets generated by loaders (like workerize-loader, the library I am updating) are being served as 404's. This happens because of the hard-coded list of output files.

[codymikol]

Thanks for the contribution! It looks like a few tests are failing unfortunately. I can take a look again if you get that fixed up.

[codymikol]

closed due to lack of feedback