Fix BatchLogProcessor

[utpilla]

Addresses #2494 (comment)

Changes

• For every export trigger, find the export target: the number of logs in the channel at the time the trigger is invoked
• Export logs until the export target is met

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

Attention: Patch coverage is 81.81818% with 4 lines in your changes missing coverage. Please review.

Project coverage is 77.9%. Comparing base (888d5a3) to head (c426db4).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
opentelemetry-sdk/src/logs/log_processor.rs	81.8%	4 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #2510   +/-   ##
=====================================
  Coverage   77.9%   77.9%           
=====================================
  Files        123     123           
  Lines      22943   22949    +6     
=====================================
+ Hits       17875   17880    +5     
- Misses      5068    5069    +1     

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