Implement more JSON-RPC Transports

[msgilligan]

Currently supported on master:

• JsonRpcClientJavaNet: HTTP using java.net.http.HttpClient
• JsonRpcClientHttpUrlConnection: HTTP using java.net.HttpURLConnection (to be deprecated?)

PRs:

• UNIX domain sockets: PR Create UNIX sockets JsonRpc client/server #78

To be implemented:

• TCP (for Electrum Protocol, etc)
• REST (for CLN Rest protocol)
• WebSocket (for Minecraft etc)

[msgilligan]

At some point it might make sense to look at (optional) alternatives to j.n.h.HttpClient.

For some complaints about j.n.h.HttpClient, see: 10 or more reasons to not use JDK’s HttpClient

Alternatives include:

• Methanol (enhancesjava.net HttpClient)
• OkHttp (which has its own set of issues)
• Apache HttpClient