[FLINK-16398] [kafka] Make Kafka ingress/egress type strings more compact

[tzulitai]

I decided to go with the pattern:

• Java ingress (egress): statefun.kafka.io/universal-ingress(egress)
• Polygplot Protobuf ingress: statefun.kafka.io/protobuf-ingress
• Polyglot generic egress: statefun.kafka.io/generic-egress

Basically, we mention "Kafka" in the namespace, to also match the artifact name org.apache.flink:statefun-kafka-io, and avoid mentioning "Kafka" over and over again in the type names.

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mvn clean verify -Prun-e2e-tests passes locally

[tzulitai]

cc @igalshilman

[igalshilman]

Thanks @tzulitai, The short strings look good to me.
Can you also take a look at the docs?
basically grep of the root directory shouldn't mention the old strings anymore, if this is indeed the case then I'm +1 to merge.

[tzulitai]

@igalshilman yup, I did a check on that.

Thanks, will merge this!