Disconnect From Secure Gateway

When disconnect operation is invoked on Avid Connector API it is
following next steps:

1. Avid Connector API sends payload with bal_to_sg_disconnect action
   to Secure Gateway;
   1. Avid Connector API is waiting (non-blocking/async) for incoming
      payload having action sg_to_gal_acknowledged;
   2. When payload received close websocket connection;
   3. Notify caller about success;