Provide an HTTPAztecRPCClient that connects to an HTTP server.

[LeilaWang]

The client takes a server url in constructor and calls the server for each method call:

class HTTPAztecRPCClient implements AztecRPCClient {
  constructor(serverUrl: string) {}

  sendTx(tx) {
    return this.server.post('aztec_sendTx', [tx]);
  }
}

Default serverUrl: localhost:45730

We should be able to generate the client and the server using the json-rpc package, which will be moved to foundation later.

[ludamad]

Going through my assigned issues, too easy to miss them :D. We simply don't do this over HTTP yet, right?