integrate pika_exporter into pika repo

[pourer]

Integrate the feature of pika_exporter into the pika repository. Exporter release with the pika version，and the exporter of each version only supports collecting pika metrics of this version.

• The first stage is to confirm the pika metrics

• Most of the pika metrics are obtained by parsing the pika's INFO command information. The Pika version is based on the latest master branch, need to confirm the metrics of this version.
• In addition to INFO command information, pika will also add metrics with command execution time and rocksdb related metrics(pika观测性支持 #1218). It is necessary to confirm the metrics details and export method of pika for these metrics.
• Group metrics for more flexible control of collection granularity.

• The second stage is to develop the program

• Coding for exporter, and combine it with pika's current deployment method.
• Pika exporter is a prometheus exporter, and the industry usually uses grafana as the display panel of prometheus, so can consider providing an out-of-the-box grafana dashboard template.
• As above, it is also possible to provide alertmanager rules template.

[kernelai]

LGTM

[AlexStocks]

1 对 metrics 指标进行分组，每个分组是否监控可以配置开关；
2 宗志在 #29 这个比较那个老的 issue 里面也提到过，能否配置告警模板，在监控工作完成之后，根据模板推进告警工作。不过告警是紧贴相关具体系统 如 zabbix 的，此项工作待议。
3 以后这种 issue，不管是题目还是内容，尽量使用英文。

[pourer]

1 对 metrics 指标进行分组，每个分组是否监控可以配置开关； 2 宗志在 #29 这个比较那个老的 issue 里面也提到过，能否配置告警模板，在监控工作完成之后，根据模板推进告警工作。不过告警是紧贴相关具体系统 如 zabbix 的，此项工作待议。 3 以后这种 issue，不管是题目还是内容，尽量使用英文。

ok

[pourer]

List pika metrics base on the latest master branch. See here
To be added: command execution time and rocksdb related metrics