Update the error codes used in KafkaEmitOperator::Connector::testConnection to use ErrorCodes::StreamProcessorKafkaConnectionError. Update the corresponding test in connection_errors.js  https://github.com/10gen/mongo/blob/master/src/mongo/db/modules/enterprise/src/streams/exec/kafka_emit_operator.cpp#L99

All Kafka connection failures should use the ErrorCodes::StreamProcessorKafkaConnectionError. This error is classified as a "retryable user error" in error_codes.yml: https://github.com/mongodb/mongo/blob/master/src/mongo/base/error_codes.yml#L805 

Currently, the error code used is an "internal error", which might send us alerts, though this issue is likely the user's fault.