prototype: each experiment manages its own arguments

[bassosimone]

This draft PR contains an attempt to implement https://github.com/ooni/probe/issues/2381. As explained by https://github.com/ooni/probe/issues/2381#issuecomment-1587813713, we consider the original issue addressed by the code in https://github.com/ooni/2023-05-richer-input/. We're keeping this PR around for a while more, because it seems it contains code we may want to merge into the master branch.