[HttpWebRequest] Add error.type for trace and metric

[vishweshbankwar]

Fixes #
Design discussion issue #

Changes

Sets error.type for trace and http.client.request.duration metric for HttpWebRequest. Spec: https://github.com/open-telemetry/semantic-conventions/blob/main/docs/http/http-spans.md#common-attributes

TODO: Document possible error.type values as suggested by spec.

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 #5034 (bea7bd5) into main (00750dd) will increase coverage by 0.22%.
The diff coverage is 74.19%.

@@            Coverage Diff             @@
##             main    #5034      +/-   ##
==========================================
+ Coverage   83.38%   83.60%   +0.22%     
==========================================
  Files         296      296              
  Lines       12440    12467      +27     
==========================================
+ Hits        10373    10423      +50     
+ Misses       2067     2044      -23     

Flag	Coverage Δ
unittests	83.60% <74.19%> (+0.22%)	⬆️

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

Files	Coverage Δ
...rumentation.Http/Implementation/TelemetryHelper.cs	83.33% <75.00%> (-4.17%)	⬇️
...plementation/HttpWebRequestActivitySource.netfx.cs	82.71% <73.91%> (-0.42%)	⬇️

... and 7 files with indirect coverage changes

[CodeBlanch]

LGTM