Remove or write documentation on how to use extends for configuration

[soulgalore]

You can come in a bad loop right now of you on the test runner extends the configuration locally, and the configuration that you extend includes the API call. Then the test, when running, will try to call the API.

We remove the API configuration when the API is called, but if we extends configuration on the testrunner server, it will still be there.

Either we can document it and write suggestions on how to deal with it, or if we can find a smart way to ignore that configuration.