Optimize the Event Guidelines for its usage with Nakadi

[tfrauenstein]

The Event Guidelines partially are designed to be generic, i.e. agnostic with respect to the Event Registry and Event Bus used to exchange events (e.g. Nakadi or AWS SQS). On the other hand Nakadi-specific aspects are distributed all over the place and there is no clear differentiation between generic parts and Nakadi specific parts. This creates inefficiencies for guideline usage and maintenance for the main use case at Zalando with 98% events being exchanged via Nakadi, while it does not really cover event exchange via other technologies line AWS SQS. For instance, it creates redundancies (e.g. Event Type schema definition in guidelines and Nakadi API spec) that tend to evolve inconsistently, and rules that are not needed (e.g. MUST use semantic versioning) since they are automated by Nakadi.

Proposal: Focus the event guidelines on Nakadi, eliminate guideline redundancies (e.g. rule 197, rule 246) with Nakadi doc and Nakadi API, inter link all documents clearly.