Add Histogram Support to STDOUT Exporter

[MrAlias]

The aggregation should be output with the bucket/count pairs being displayed to the user.

[mujtaba-ahmed12]

@MrAlias I would like to take this issue.

[jmacd]

This could use the format embraced by Prometheus for the boundaries as "le" labels.

The upper boundary at 1 is encoded as a label "le=1" in this scheme.

[MrAlias]

This could use the format embraced by Prometheus for the boundaries as "le" labels.

The upper boundary at 1 is encoded as a label "le=1" in this scheme.

Given our existing JSON structure here I had originally though something like:

type expoLine struct {
	Name      string      `json:"name"`
...
	Histogram []bucket    `json:"histogram,omitempty"`
}

type boundary struct {
	Min float64 `json:"min"`
	Max float64 `json:"max"`
}

type bucket struct {
	boundary `json:"bounds"`
	Count    float64 `json:"count"`
}

But, I wonder if we couldn't also have a form of the exporter export prometheus metrics. They are text based and well known.

Maybe add as option like PrettyPrint?

[MrAlias]

Resolved by #3175