End-to-end tests

[lovromazgon]

We need to create end-to-end tests that treat Conduit as a black box, trigger requests to the API and make sure they produce the expected result. For now they should cover at least the main paths (e.g. creating a pipeline, starting it, stopping it, deleting it). These tests should be easy to run locally without setting up a specific environment (ideally with one make target), additionally we should trigger the tests in the CI as regression tests before merging any PR.

[dylanlott]

This ticket should not touch UI end to end tests, only the Conduit server end to end testing.