[Shims.OpenTracing] deprecate package

[Kielek]

Handles open-telemetry/opentelemetry-specification#4938

Changes

Deprecates Shims.OpenTracing.
The key dependency was released in 2019 and is now fully abandoned: https://www.nuget.org/packages/OpenTracing#versions-body-tab

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, 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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.65%. Comparing base (5b37145) to head (d26e154).
⚠️ Report is 9 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6976      +/-   ##
==========================================
- Coverage   88.68%   88.65%   -0.04%     
==========================================
  Files         263      263              
  Lines       12397    12397              
==========================================
- Hits        10994    10990       -4     
- Misses       1403     1407       +4     

Flag	Coverage Δ
unittests-Project-Experimental	88.44% <ø> (-0.18%)	⬇️
unittests-Project-Stable	88.45% <ø> (-0.02%)	⬇️
unittests-UnstableCoreLibraries-Experimental	42.23% <ø> (+0.53%)	⬆️

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

Files with missing lines	Coverage Δ
src/OpenTelemetry.Shims.OpenTracing/TracerShim.cs	91.66% <ø> (ø)

... and 1 file with indirect coverage changes