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;