feat(testing): Full integration tests

[johausmann]

We can use our web server to emulate remote URLs. By placing test data in the environment, we can perform full integration tests on the OBLX pipeline. To do this, all URLs need to be configurable for testing.

[jonasfreimuth]

Slightly related: As suggested in this workflow catalog issue, if we could remove the need for the storage plugin during testing, many things would be simpler.