Post Channel Message

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

1. Avid Connector API sends payload with bal_to_sg_post 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 it
      checks metadata→runtime→errorType;
      1. If errorType doesn’t exist, notify caller about success;
      2. If errorType was provided, notify caller about corresponding
         failure;