update kafka docs and defaults to v2.0.0

[Dieterbe]

No description provided.

[Dieterbe]

we should also update all configs and built-in defaults to use kafka version v2.0

[codelingo]

LGTM

[Dieterbe]

I have:

1. updated https://hub.docker.com/r/raintank/kafka to make latest point to v2 (commands used docker tag raintank/kafka:v2.0.0 raintank/kafka:latest && docker push raintank/kafka:latest). no need to update docker stack configs because they all already use "latest"
2. updated kafka-version = 2.0 for both kafka plugins in all configs and built-in defaults
3. tested in docker-dev-custom-cfg-kafka with offset oldest and newest (and fakemetrics). behaves fine

I think this should do it. @robert-milan anything else I forgot? I thought our config file(s) had other settings related to kafka version, but apparently not.

[woodsaj]

no need to update docker stack configs because they all already use "latest"

existing users will need to run docker pull raintank/kafka to have their local image updated to the new version.

[Dieterbe]

@woodsaj sure but does that mean anything should change in this PR?

[woodsaj]

Nope, just drawing attention to the fact.