This diff makes the implementation of the engine package more abstract by changing HTTPClient() to return a model.HTTPClient as opposed to returning an *http.Client. Part of https://github.com/ooni/probe/issues/2184
Package github.com/ooni/probe-engine/probeservices
This package contains code to contact OONI probe services.
The probe services are HTTPS endpoints distributed across a bunch of data centres implementing a bunch of OONI APIs. When started, OONI will benchmark the available probe services and select the fastest one. Eventually all the possible OONI APIs will run as probe services.