HttpSemanticConventions - new metric in HttpClient Instrumentation

[TimothyMothra]

Towards #4484

This PR adds the new http.client.request.duration metrics in the HttpClient Instrumentation library.

Changes

• all the following changes are made behind the environment variable OTEL_SEMCONV_STABILITY_OPT_IN
• update Instrumentation.Http class HttpHandlerMetricsDiagnosticListener to emit new metric.
  • http.client.duration (milliseconds) replaced with http.client.request.duration (seconds)
    This is defined in the as-of-yet unreleased v1.22.0 https://github.com/open-telemetry/semantic-conventions/blob/main/docs/http/http-metrics.md
• Test changes
  • HttpClientTests renamed to HttpClientTests.Old. new classes HttpClientTests.New and HttpClientTests.Dupe.
    This covers all options of the environment variable.
  • http-out-test-cases.json renamed to http-out-test-cases_Old.json. new files http-out-test-cases_New.jsonandhttp-out-test-cases_Dupe.json`
    These files hold all test cases for the previous test classes.
  • HttpClientTests.Basic was updated to accommodate 3 json files.

Merge requirement checklist

• CONTRIBUTING guidelines followed (nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

Merging #4891 (236485f) into main (0b2d036) will increase coverage by 0.39%.
Report is 6 commits behind head on main.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #4891      +/-   ##
==========================================
+ Coverage   82.88%   83.27%   +0.39%     
==========================================
  Files         294      294              
  Lines       12200    12211      +11     
==========================================
+ Hits        10112    10169      +57     
+ Misses       2088     2042      -46     

Flag	Coverage Δ
unittests	83.27% <100.00%> (+0.39%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...ementation/HttpHandlerMetricsDiagnosticListener.cs	97.50% <100.00%> (+20.35%)	⬆️

... and 10 files with indirect coverage changes

[CodeBlanch]

@TimothyMothra I think there's too much duplication of code going on in these tests. I tried to clean it up on #4870. Can you help me get that PR reviewed & merged and then can we apply this on top of that?

[TimothyMothra]

@TimothyMothra I think there's too much duplication of code going on in these tests. I tried to clean it up on #4870. Can you help me get that PR reviewed & merged and then can we apply this on top of that?

I'll take a look at the other PR today. I was about to pull some of the test changes out of THIS PR and create a smaller test refactor PR. I'll review your changes before I go down this path :)

[TimothyMothra]

Converting this to Draft. I think #4870 is going to merge first. If there are too many merge conflicts, it might easier to recreate this PR.