karma-runner: stop using raw cli options

[nicojs]

The current way of running Karma is deprecated. When running the integration tests you can see it:

 21 04 2021 17:32:20.977:WARN [runner]: Passing raw CLI options to `runner(config, done)` is deprecated. Use `parseConfig(configFilePath, cliOptions, {promiseConfig: true, throwErrors: true})` to prepare a processed `Config` instance and pass that as the `config` argument instead.

Let's do exactly what they specify in this warning to fix this.

Note: We might need to still send raw options for older versions of Karma. We'll have to see. We can start with the new implementation, since we have an e2e test for the oldest supported karma version.