add prometheus metric exporter framework

[hangc0276]

Motivation

KOP doesn't expose prometheus metrics to monitor running stats, which will be hard the debug performance problem.

Changs

1. add Prometheus metrics provider for kop and use individual port to expose kop metrics
2. Due to BookKeeper Prometheus metric provider include basic metrics stats, such as jvm metrics, memory metrics, cpu metric etc, which will lead those metrics register twice. When run kop with pulsar broker, the prometheus metric thread will start failed.

[codelipenghui]

@hangc0276 We can expose metrics through /metrics endpoint of the broker directly, I have add Raw Metrics Provider in Pulsar (apache/pulsar#9021), you can use it to expose additional metrics to the broker metrics endpoint.

[BewareMyPower]

The kafka-impl/conf won't be used anymore (see #387 ), please edit docs/configuration.md or add a new document for exposing metrics to Prometheus under docs directory and add a link in README.md.

[hangc0276]

@hangc0276 We can expose metrics through /metrics endpoint of the broker directly, I have add Raw Metrics Provider in Pulsar (apache/pulsar#9021), you can use it to expose additional metrics to the broker metrics endpoint.

@codelipenghui Ok, I update the code and use pulsar raw metrics provider to expose kop metrics to pulsar metrics group. Please take a look. Thanks.

[BewareMyPower]

You should fix the code style first. Then please remove kafka-impl/conf/broker.conf. It's unused.

Regarding how to enable the monitor for prometheus, we can open a new PR to add the docs.

[jiazhai]

opened a new issue for the doc. @codelipenghui @BewareMyPower Would you please help review it again?

[BewareMyPower]

Suggested change

String SERVER_STATUS = "SERVER_STATUS";

[BewareMyPower]

Remove unused variable

[BewareMyPower]

I've left a few comments, PTAL.

[hangc0276]

I've left a few comments, PTAL.

@BewareMyPower OK， i will fix it