chore: Prepare for release v0.31.0

[lalitb]

Fixes #
Design discussion issue (if applicable) #

Changes

Please provide a brief description of the changes here.

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

❌ Patch coverage is 91.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.5%. Comparing base (9cde968) to head (5284329).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
opentelemetry-http/src/lib.rs	91.6%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #3179     +/-   ##
=======================================
- Coverage   80.7%   80.5%   -0.2%     
=======================================
  Files        126     126             
  Lines      22305   22238     -67     
=======================================
- Hits       18007   17921     -86     
- Misses      4298    4317     +19     

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