feat(NimBLEClient): allow connection id / established flag to be set via public API.

[finger563]

This PR replaces #152

Main use case is to allow an easy mechanism for GATT Servers to read the name of connected clients by passing their connection info to the Client class.

Example (from espp::BleGattServer):

  std::string get_connected_device_name(NimBLEConnInfo &conn_info) {
    if (!server_) {
      logger_.error("Server not created");
      return {};
    }
    if (!client_) {
      logger_.error("Client not created");
      return {};
    }

    // since this connection is handled by the server, we won't manually
    // connect, and instead inform the client that we are already connected
    // using this conn handle
    client_->clearConnection(); // make sure any previous connection state is cleared
    client_->setConnection(conn_info);

    // could alternatively use:
    // client_->clearConnection();
    // client_->setConnection(conn_info.getConnHandle(), conn_info.getAddress());

    // refresh the services
    client_->getServices(true);
    // now get Generic Access Service
    auto gas = client_->getService(NimBLEUUID("1800"));
    if (!gas) {
      logger_.error("Failed to get Generic Access Service");
      return {};
    }
    // now get the Device Name characteristic
    auto name_char = gas->getCharacteristic(NimBLEUUID("2A00"));
    if (!name_char) {
      logger_.error("Failed to get Device Name characteristic");
      return {};
    }
    // make sure we can read it
    if (!name_char->canRead()) {
      logger_.error("Failed to read Device Name characteristic");
      return {};
    }
    // and read it
    return name_char->readValue();
  }

[finger563]

Looks good, thanks! Have you tested this with the changes?

Yup, I've tested my changes locally in espp:

With the output from espp/components/hid_service/example:

Showing that the code to get the remote device name using this code is good :)