Copy/paste artifact in the Consuming Null Payloads docs

[artembilan]

See more info in the https://docs.spring.io/spring-pulsar/docs/1.1.0-RC1/reference/reference/tombstones-reactive.html#tombstones-reactive.consume.

The table talks about Flux<org.apache.pulsar.client.api.Messages<T>> where it feels like this has to be Flux<org.springframework.messaging.Message<T>>. Although, that indeed rises the question how about org.apache.pulsar.client.api.Messages in reactive manner...