feat(deltachat-rpc-server): add --openrpc option

[link2xt]

This is not exactly the implementation of #4412, but is even easier to use, the server does not even need to be started. rpc.discover method may be automatically added by yerpc in a later version as well for e.g. remote usage over a socket or something like this, but this is not currently needed.

openrpc.json is no longer generated by tests, use deltachat-rpc-server --openrpc >openrpc.json instead.

[link2xt]

My idea with this rpc.discover and --openrpc option is to read the OpenRPC specification by the Python code and generate Rpc class methods dynamically. This way we can get autocompletion and help() for RPC methods in REPL without generating Python source code and having any autogenerated files at all.

cc @hpk42 @flub Maybe you have an opinion on how well this would work with Python. I have tried a bit how defining attributes dynamically works with python-mode in Emacs and it seems autocompletion does not care about attributes defined in the REPL with setattr even though they are visible in dir() of the object. But in Jupyter Notebook this works:

So with a proper editor support this is possible, but I wonder what setup can we recommend for Emacs, VIM and Visual Studio Code?