Treat differently OperationCanceledException raised as the result of cancellation initiated by the client.

### Is your feature request related to a problem? Please describe.
When a client cancels the request, I see message logged `{Id: 17, Name: 'ErrorSendingMessage'}`. IMO, while still being an exception, it should not be treated as an error per se. 

### Describe the solution you'd like
I'd prefer to have a separate event. `MessageNotSentOperationCancelled`
