Control Plane Adapter callback integration

[wolf4ood]

What

In EDC upstream there has been some work for supporting callbacks in the state machines, in particular in the Contract Negotiation process and in the Transfer process.
We should integrate in the callback system and provide a simplified API for "opening" a Transfer with only one request.

The output of the "opening" a transfer will be an EDR store in the CPA which will come in future PR. For now it will just
fire a transfer request of type HttpProxy and if an EDR receiver is configured it will be called.

Why

Simplification of the Control plane adapter without breaking the semantics of EDC.