update parser to parse from prometheus txt metrics data

[tomsun28]

What's changed?

Checklist

• I hereby agree to the terms of the HertzBeat CLA
• I have read the Contributing Guide
• I have written the necessary doc or comment.
• I have added the necessary unit tests and all cases have passed.

Add or update API

• I have added the necessary e2e tests and all cases have passed.

[Ceilzcx]

这个为什么改了？

[tomsun28]

@Ceilzcx 参考了下 victoriametrics 的指标存储结构，

# TYPE jvm_gc_pause_seconds summary
jvm_gc_pause_seconds{action="end of minor GC",cause="Metadata GC Threshold",quantile="0.0",} 0.0
jvm_gc_pause_seconds{action="end of minor GC",cause="Metadata GC Threshold",quantile="0.25",} 0.0
jvm_gc_pause_seconds{action="end of minor GC",cause="Metadata GC Threshold",quantile="0.5",} 0.0
jvm_gc_pause_seconds{action="end of minor GC",cause="Metadata GC Threshold",quantile="0.75",} 0.0
jvm_gc_pause_seconds{action="end of minor GC",cause="Metadata GC Threshold",quantile="1.0",} 0.0

类似这种 summary 类型的指标也把quantile这种看成普通标签，不做特殊处理，在插入 victoriametrics 或其它数据库的格式也就统一类似如下，标签+指标值：

{
  // metric contans metric name plus labels for a particular time series
  "metric":{
    "__name__": "metric_name",  // <- this is metric name

    // Other labels for the time series

    "label1": "value1",
    "label2": "value2",
    ...
    "labelN": "valueN"
  },

  // values contains raw sample values for the given time series
  "values": [1, 2.345, -678],

  // timestamps contains raw sample UNIX timestamps in milliseconds for the given time series
  // every timestamp is associated with the value at the corresponding position
  "timestamps": [1549891472010,1549891487724,1549891503438]
}

prometheus 查询展示的结构也如下：

[Ceilzcx]

ci not pass