PR Review feedback

PR Review feedback over [slack](https://form3.slack.com/archives/C02281GJCJF/p1669986912679049).

Currently there are already users who are performing error string
comparision for this use case. To avoid introducing a breaking change
until there is a better way of handling these error messages, we will
retain the error message for the newly introduced canonical error
value.

jserrors.go

@@ -102,7 +102,7 @@ var (
 	ErrConsumerDeleted JetStreamError = &jsError{message: "consumer deleted"}
 
 	// ErrConsumerLeadershipChanged is returned when pending requests are no longer valid after leadership has changed
-	ErrConsumerLeadershipChanged JetStreamError = &jsError{message: "leadership changed"}
+	ErrConsumerLeadershipChanged JetStreamError = &jsError{message: "Leadership Changed"}
 
 	// DEPRECATED: ErrInvalidDurableName is no longer returned and will be removed in future releases.
 	// Use ErrInvalidConsumerName instead.