If you install multiple instances of exporter to monitor
multiple kafka clusters, each serviceMonitor will scrape
all instances regardless of the different installation name.
for eg:
```
helm install kafka-exporter-cluster1 ./kafka-exporter
helm install kafka-exporter-cluster2 ./kafka-exporter
```
because the instance name, in this case the installation name,
is the only differentiator in these installations are absent in
the serviceMonitor selector, serviceMonitor will all instances.

Signed-off-by: Rajesh Rajendran <[email protected]>

1. Adding zookeeper endpoints
2. Adding additional flags can be given via values.yaml
for eg:
```
kafkaExporter:
  zookeeper:
    servers:
      - kafka-1-cp-zookeeper.kafka-1.svc.cluster.local:2181
  kafka:
    servers:
      - kafka-1-cp-kafka.kafka-1.svc.cluster.local:9092
  additionalFlags:
    - --use.consumelag.zookeeper

```

Signed-off-by: Rajesh Rajendran <[email protected]>

- broker unavailable
- ISR sync issue
- Kafka leader abnormal change

Signed-off-by: Rajesh Rajendran <[email protected]>