Json rpc server

[kylegranger]

Ok, I'm about as far as I can go with this, feature-wise (there's not a whole lot to it as it is right now). Obviously, feedback for any features I'm missing is most welcome. This object will probably also evolve as we start using it. Some notes.

• the code in main.cpp will NOT be merged ! It just shows how it currently is used (which is also indeed food for a review) Next up, I'll do a readme doc, and move the code examples into there, with other necessary information
• the server listens on localhost, at the port passed in (arbitrarily set now to 2584).
• runs on top of the io_service from client runner, using web sockets. Only that and HTTP are valid for Polkadot -- definitely no TCP.
• caller accesses the packio server, and then adds handlers.
• for integration of the packio library with our app, cmake clones package, and patches it, in the end, fairly simple. Patches were necessary because as Conan project it required Boost 1.75, and it would not build with 1.80. Patch also has tweaks to a couple logging texts, and access to our logger.
• packio is a header-only library, so I have a logger instantiation in utils (new packio_logger). This is one of those cases 'there are many ways to Rome'. Happy to hear other ideas.
• the tests check correct request/response (using node websocket client), and connect status.
• nothing fails with the ASAN flag.

[kylegranger]

Thinking about the connect(), and really, that should always succeed. If it fails setting up server on localhost, we should log an error and exit() with failure.

[kylegranger]

two more notes:

• don't know why clang CI is failing (I'll confirm gcc builds on Linux). It's on an asio undefined. I'll investigate.
• I'm going to remove the ip address, which is really not needed (we always listen from localhost/127.0.0.1)

[kylegranger]

converted to draft pending linux-clang build fixes.

[kylegranger]

Opening again for review. New changes:

• No ip address, since we always connect to local host (127.0.0.1)
• No connect state, we always succeed.
• Demo handlers are in a new readme in /docs.
• Fix for a CI build problem. The problem was Boost not being enabled for coroutines. But this was only a problem with the Linux clang build (running on ubuntu, was well as in the CI). MacOS-clang and the CI-gcc both successfully built. The solution was to add a compiler define, BOOST_ASIO_HAS_CO_AWAIT.

[kylegranger]

This is status of the server when I stopped development:

• the packio library has been replaced by a boost::asio websocket server.
• when a client connects, a websocket_session is instantiated, and a callback creates a client in the server, stored in a map.
• when the websocket closes, another call back happens, and the server removes the client from its map.
• a received message gets passed up to the server. Right now, it's just dumped to the console. Mapping the message to the correct client happens via an id in the websocket session.
• there is a server method defined to register a handler (not implemented), and a map of handlers.

Implementing the JSON-RPC messaging is just a matter of:

• parsing the JSON message to a boost ptree
• check well-formed message, check for method and params
• use method to fetch handler, send the client and params to handler