[SPARK-3887] Send stracktrace in ConnectionManager error replies

When reporting that a remote error occurred, the ConnectionManager should also log the stacktrace of the remote exception. This PR accomplishes this by sending the remote exception's stacktrace as the payload in the "negative ACK / error message."
I suppose that this could break if we added another message type and used it to report errors.  Do you think that I should pre-emptively add error handling code around this?