Minor update to stdout exporter example to show log correlation

[cijothomas]

Stdout example modified to emit a log within span context to show how correlation works.
Fix stdout to print TraceFlags.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 76.8%. Comparing base (3694ff9) to head (1f48b70).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
opentelemetry-stdout/src/logs/exporter.rs	0.0%	3 Missing ⚠️
opentelemetry-stdout/src/trace/exporter.rs	0.0%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #2459     +/-   ##
=======================================
- Coverage   76.9%   76.8%   -0.1%     
=======================================
  Files        122     122             
  Lines      22213   22217      +4     
=======================================
  Hits       17082   17082             
- Misses      5131    5135      +4     

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