refactor: refactor Baggage with Context interaction

[gruebel]

Relates to #2717 point 6

Changes

• with_baggage() and current_with_baggage() now only accept a Baggage instance and override any existing Baggage in the Context
• added a private BaggageContextValue to hide the direct retrieval of Baggage from Context to make sure it needs to accessed via context.baggage()

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

All modified and coverable lines are covered by tests ✅

Project coverage is 79.6%. Comparing base (baf4bfd) to head (4fc5f1c).
Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #2748   +/-   ##
=====================================
  Coverage   79.6%   79.6%           
=====================================
  Files        123     123           
  Lines      23041   23034    -7     
=====================================
  Hits       18356   18356           
+ Misses      4685    4678    -7     

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[lalitb]

LGTM with nit comment here.