Add Support for HttpSemanticConvention breaking changes.

[TimothyMothra]

Design discussion issue #4484

Http Semantic Convention is introducing breaking changes.
This PR introduces a new helper class to read and parse the new environment variable.

During startup, an instrumentation library should check for an environment variable.
Based on the parsed value, that library will either emit the old attributes, new attributes, or both.

Changes

• Add Helper class to parse environment variable
• Add enum to represent Semantic Convention decision.
• Add unit tests to validate Parser and Enum Flags.
• Update HttpInListener ctor in Instrumentation.AspNetCore

Please provide a brief description of the changes here.

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)

[TimothyMothra]

@vishweshbankwar please review

[codecov]

Codecov Report

Merging #4504 (637c9bd) into main (f4f4469) will increase coverage by 0.01%.
The diff coverage is 81.81%.

❗ Current head 637c9bd differs from pull request most recent head 4ca4063. Consider uploading reports for the commit 4ca4063 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4504      +/-   ##
==========================================
+ Coverage   85.16%   85.17%   +0.01%     
==========================================
  Files         316      317       +1     
  Lines       12583    12594      +11     
==========================================
+ Hits        10716    10727      +11     
  Misses       1867     1867              

Impacted Files	Coverage Δ
...metry.Api/Internal/HttpSemanticConventionHelper.cs	80.00% <80.00%> (ø)
...tation.AspNetCore/Implementation/HttpInListener.cs	90.18% <100.00%> (+0.06%)	⬆️

... and 1 file with indirect coverage changes

[vishweshbankwar]

LGTM

[alanwest]

LGTM, just one more minor thing

[alanwest]

just one more nit. use a file-scoped namespace here to reduce indentation

[TimothyMothra]

no problem!

any way to make this a code style rule for future PRs?

[utpilla]

We should also update the existing classes to use file-scoped namespace for being consistent.