async createNew(connection, user) {
    const connectionClient = new ConnectionClient(connection, user);
    await connectionClient.connect();
    connectionClient.scheduleCleanupInterval();
    this.connectionClients.push(connectionClient);
    return this.getOneById(connectionClient.id);
  }
Create new connection client and connect
@param {object} connection
@param {object} user
@returns {ConnectionClient}