PoC of KafkaAgent in Strimzi for exposing metrics

What

Create a PoC of KafkaAgent in Strimzi for exposing metrics via Jetty. It's a prework for ENTMQST-3931.

Why

To make the Kafka Roller aware of broker state that're not exposed via the Kafka Admin API or Kubernetes API, we need a broker side component which reads the broker state and exposes an API for metric collections.

How

Some POC [1] by tbentley-1 could be used as starting point of such an integration in Strimzi.

 [1] https://github.com/tombentley/ksense/blob/main/agent/src/main/java/com/github/tombentley/ksense/agent/StatusEndpoints.java
[2] https://github.com/strimzi/strimzi-kafka-operator/tree/main/kafka-agent