[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."

Author: Josh Rosen <joshrosen@apache.org>

Closes #2741 from JoshRosen/propagate-cm-exceptions-to-sender and squashes the following commits:

b5366cc [Josh Rosen] Explicitly encode error messages using UTF-8.
cef18b3 [Josh Rosen] [SPARK-3887] Send stracktrace in ConnectionManager error messages.