errors: make errProducerIDLoadFail retriable

When a producer id load fails with a retriable error, we swallow the
error and instead return errProducerIDLoadFail. This gets used when
bumping repeated load failures on partitions, and since this internal
error does not look retriable, we fail records.

We now make this a retriable broker error (since it is), which allows
the producer ID load to fail and be retried.

pkg/kgo/errors.go

@@ -51,6 +51,11 @@ func isRetriableBrokerErr(err error) bool {
 	if isNetClosedErr(err) || errors.Is(err, io.EOF) {
 		return true
 	}
+	// We could have a retriable producer ID failure, which then bubbled up
+	// as errProducerIDLoadFail so as to be retried later.
+	if errors.Is(err, errProducerIDLoadFail) {
+		return true
+	}
 	// We could have chosen a broker, and then a concurrent metadata update
 	// could have removed it.
 	if errors.Is(err, errChosenBrokerDead) {