[Instrumentation.SqlClient] Move to contrib repository

[Kielek]

Towards: #5526
Related to: open-telemetry/opentelemetry-dotnet-contrib#1673

Changes

[Instrumentation.SqlClient] Move to contrib repository

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)

[Kielek]

Pull request in the contrib repository already merged.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.46%. Comparing base (6250307) to head (682a459).
Report is 191 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5559      +/-   ##
==========================================
+ Coverage   83.38%   85.46%   +2.08%     
==========================================
  Files         297      282      -15     
  Lines       12531    12216     -315     
==========================================
- Hits        10449    10441       -8     
+ Misses       2082     1775     -307     

Flag	Coverage Δ
unittests	?
unittests-Instrumentation-Experimental	83.95% <ø> (?)
unittests-Instrumentation-Stable	83.87% <ø> (?)
unittests-Solution-Experimental	85.39% <ø> (?)
unittests-Solution-Stable	85.22% <ø> (?)
unittests-Unstable-Core	19.87% <ø> (?)

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see 80 files with indirect coverage changes