Semantic Convention changes. correct link and update changelog.

[TimothyMothra]

Design discussion issue #4484

Changes

• correct the link to semantic conventions, using new repo.
• update Changelog with semcon version number
• update Changelog with missing links to PRs.

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 #4655 (612e01a) into main (1d1c714) will decrease coverage by 0.03%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4655      +/-   ##
==========================================
- Coverage   85.01%   84.99%   -0.03%     
==========================================
  Files         314      314              
  Lines       12715    12715              
==========================================
- Hits        10810    10807       -3     
- Misses       1905     1908       +3     

Impacted Files	Coverage Δ
...tation.AspNetCore/Implementation/HttpInListener.cs	90.47% <ø> (ø)
...AspNetCore/Implementation/HttpInMetricsListener.cs	64.70% <ø> (ø)
src/Shared/HttpSemanticConventionHelper.cs	80.00% <ø> (ø)

... and 2 files with indirect coverage changes