Observation implementation

What

Create a broker observation abstraction and implementation to allow collecting various information about the broker from different sources such as Kubernetes (Pod status etc), Kafka Admin API (ISR state etc) and metrics endpoints.

Why

The rich observations enables a sophisticated classification of the broker status which more accurately reflects its state.

How

The KR2 prototype introduced an Observer abstraction and implementation.

• Validate the prototype and interfaces and suggest any improvements
• Work your way to a full implementation based on the Kubernetes API & Admin API that's validated with multiple test cases and needed mocks