Cumulative acknowledgement for multi-topic subscription

[iradul]

This is most likely upstream issue but cumulative acknowledgement doesn't seem to be working when subscribed to multiple topics.

[equanz]

This is most likely upstream issue

I think so too. This is C++ library issue.
Currently, C++ library doesn't support Cumulative Ack for multi topics consumer.
https://github.com/apache/pulsar/blob/v2.7.0/pulsar-client-cpp/lib/MultiTopicsConsumerImpl.cc#L574-L576
apache/pulsar#6796