Http Request Duration Histogram should be in seconds unit

[Zslow]

Hi,
I changed the units of the Http Request Duration Histogram to Seconds.
Here's a link to the official Prometheus documentation where states that base units should be used for any metric, as a best practice.

https://prometheus.io/docs/practices/naming/#metric-names

We are testing this adapter on a project and needed the metric with the right unit in order to know if http requests are being lost.

Thank You.

[codecov]

Codecov Report

Merging #106 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #106   +/-   ##
=======================================
  Coverage   13.18%   13.18%           
=======================================
  Files           4        4           
  Lines         622      622           
=======================================
  Hits           82       82           
  Misses        525      525           
  Partials       15       15

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