Preparation for renku-python 1.0

[rokroskar]

This epic is for keeping track of the technical implementations that need to happen in order for the new version of renku-python to be used as a part of renkulab.

A decision was made to investigate the possibility of running two versions of the renku core service (i.e. the service part of renku-python) side-by-side with the gateway routing requests based on the headers. The UI would check the state of the project to determine which API to request.

We expect the majority of projects to have entirely non-problematic migrations that take a few seconds. For larger projects, we will provide guidance in the UI about how to migrate manually.