fix(karma-webpack): allow `filename` and `chunkFilename` to be overridden (`config.output`)

[Teamop]

Please check if the PR fulfills these requirements

• [ ] Tests for the changes have been added (for bug fixes / features)
• [ ] Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

• [x] Bugfix
• [ ] Feature
• [ ] Code style update (formatting, local variables)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [ ] CI related changes
• [ ] Other... Please describe:

What is the current behavior? (You can also link to an open issue here)

What is the new behavior? same PR as #336 against the next branch

Does this PR introduce a breaking change?

• [ ] Yes
• [x] No

If this PR contains a breaking change, please describe the following...

• Impact:
• Migration path for existing applications:
• Github Issue(s) this is regarding:

Other information:

[michael-ciniawsky]

I'm sry to have bothered you here, I'm an idiot and thought v3.0.0 was already on it's own branch which wasn't the case. This PR is now obsolete since I needed to rebase anyways :). My apologies again

[Teamop]

Don't worry about it, thanks @michael-ciniawsky