Add measurement attributes in Prometheus time series data for Histogram

[lalitb]

Fixes #1437 , #1432

Changes

Add measurement attributes in Prometheus time series data for Histogram.
The sample data generated would be:

prometheus_metric_example_count{key1="value1",key4="value4"} 0 1654821769617
prometheus_metric_example_sum{key1="value1",key4="value4"} 0 1654821769617
prometheus_metric_example_bucket{key1="value1",key4="value4",le="0"} 0 1654821769617
prometheus_metric_example_bucket{key1="value1",key4="value4",le="5"} 0 1654821769617
prometheus_metric_example_bucket{key1="value1",key4="value4",le="10"} 0 1654821769617
prometheus_metric_example_bucket{key1="value1",key4="value4",le="25"} 0 1654821769617
prometheus_metric_example_bucket{key1="value1",key4="value4",le="50"} 0 1654821769617
prometheus_metric_example_bucket{key1="value1",key4="value4",le="75"} 0 1654821769617
prometheus_metric_example_bucket{key1="value1",key4="value4",le="100"} 0 1654821769617
prometheus_metric_example_bucket{key1="value1",key4="value4",le="250"} 0 1654821769617
prometheus_metric_example_bucket{key1="value1",key4="value4",le="500"} 0 1654821769617
prometheus_metric_example_bucket{key1="value1",key4="value4",le="1000"} 0 1654821769617
prometheus_metric_example_bucket{key1="value1",key4="value4",le="+Inf"} 0 1654821769617

where key1="value1",key4="value4" are the measurement attributes, and le="xx" are the buckets.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[codecov]

Codecov Report

Merging #1440 (87320e8) into main (6ee70a7) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1440   +/-   ##
=======================================
  Coverage   84.89%   84.89%           
=======================================
  Files         154      154           
  Lines        4373     4373           
=======================================
  Hits         3712     3712           
  Misses        661      661