rgw/kafka: do not destroy the connection on errors

rgw/kafka: do not destroy the connection on errors

as well as other simplifications:
* do not store temporary configuration in the connection object. just
  use as a local variable
* do not create a connection without a producer

other improvements:
* copy to a local list before publishing
* convert internal error codes to errno

Fixes: https://tracker.ceph.com/issues/66017
Signed-off-by: Yuval Lifshitz <ylifshit@ibm.com>
(cherry picked from commit 1b6e8501565972bc833118a3fe34ef2f43f400ad)

 Conflicts:
	src/rgw/rgw_kafka.cc