Add support for Kafka 2.6

Kafka 2.4 introduced the static membership [KIP-345|https://cwiki.apache.org/confluence/display/KAFKA/KIP-345%3A+Introduce+static+membership+protocol+to+reduce+consumer+rebalances]

So i propose to add a Publish/Consume 2_5 with the last Kafka Client 2.5. 

I don't know the versioning strategy for Kafka Processors. We have 2 choices : 

• Thanks to dynamic properties, upgrading the 2.0 processors set with 2.5 kafka libs (confusing but lazy update)
• Create a new 2.5 processors set

I've created a PR with the second choice : A new 2.5 processors set.