Allow requesting config state from backend

[choden-dev]

Overview

Allows the client to send a message requesting the current saved client config. Currently relies on querying the db, will need to investigate if it is worth having in memory

Example usage (see messaging/examples/client_sending_key_config_to_server.rs):

  handler.request_server_config().unwrap();
  let result = handler.check_for_server_config().unwrap();
  println!("{:?}", result);