[CONFIGURATION] Apply default sampler when none is specified

[RaviTriv]

Fixes #4034

Changes

PR to apply default sampler when one is not set in the trace provider configuration. Updated the parser to apply ParentBasedSamplerConfiguration with AlwaysOnSamplerConfiguration as per the spec when no sampler is specified.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.83%. Comparing base (d6035a8) to head (07322f1).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4170      +/-   ##
==========================================
+ Coverage   82.82%   82.83%   +0.01%     
==========================================
  Files         406      406              
  Lines       16913    16917       +4     
==========================================
+ Hits        14007    14011       +4     
  Misses       2906     2906              

Files with missing lines	Coverage Δ
sdk/src/configuration/configuration_parser.cc	77.63% <100.00%> (+0.07%)	⬆️

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