Config flag to suppress sending the username in the port call update request to Veslink

Create a config flag (or other means) to suppress sending the Username in the port call update request to Veslink/DA-Desk. This is required so that the original operator will remain for the entire port call in DA-Desk.
With the current setup, the voyage operator is sometimes changed, with the result that the original PDA is re-assigned to the new operator, which is incorrect. The original operator should remain assigned to the previously made port call(s), but the new operator should then be assigned to any new DAs for existing (e.g., FDA) or new (PDA, FDA, etc.) port calls.