In a pure step-by-step model, we don't need to trace HTTP round trips like we did before. We _may_ want in the future to also have some form of HTTP tracing (see https://github.com/ooni/probe-cli/pull/868 for a prototype) but doing that is currently not in scope for moving forward the step-by-step design. For this reason, I only added a public convenience function for formatting an OONI spec compatible request. I also added new fields, which should be documented inside the ooni/spec repository (see https://github.com/ooni/probe/issues/2238).
Required by https://github.com/ooni/probe/issues/2237
