feat: use new solvers schema for driver <> solver_engine interface

[fleupold]

Problem

The legacy instance.json format is terribly redundant, full of inconsistencies and unnecessary fields and was refactored during the solver-driver colocation project in favour of a new/cleaner interface between driver and solver_engines (https://github.com/cowprotocol/services/blob/a72c4c374afea785929a0a0a98d7840faf3df34c/crates/solvers/openapi.yml)

Suggested solution

Explain the problem/result file in terms of the new data model and mark the existing document as deprecated (or remove altogether)

Alternatives considered

Keep maintaining the old json (but I think that's a bad idea)

[mfw78]

In regards to scoping for this, would this be a joint effort between backend and solvers?

[fleupold]

I think it should be driven by the solver team with the backend team providing clarification and help where needed. The interface itself is documented using swagger (and in code).
Maybe @fhenneke's test solver from dappcon could be adopted to work with the new interface.

[fhenneke]

One thing blocking me from changing the documentation is that the code and api specification for the new interface are inconsistent, see this issue.
I suppose the rust code is the reference then. But I am not familiar enough with it to derive the format of request and response.