Description
We currently have ISessionProvider in renku.domain_model and implementations of it in renku.core.session that get used as plugins.
While the concept of a "session" is renku specific and makes sense to have as a domain model, the backends dealing with the session (Docker/Notebook Services) are not renku-python specific and as such should be treated as external infrastructure and properly wrapped/injected. They are a bit unusual since pluggy takes care of injection instead of the inject library, but the concept is the same.
So we should move ISessionProvider to renku.core.interface and the DockerSessionProvider and RenkulabSessionProvider to renku.infrastructure (maybe in a session subfolder).
The renku.core.session.session code itself is fine and can stay where it is.