Cleanup initialization order for exporterhelper

[bogdandrutu]

Also, this PR fixes a concurrency data issue that only affects users that manually turned on exporter.UsePullingBasedExporterQueueBatcher featuregate.

exporter.UsePullingBasedExporterQueueBatcher is still alpha in the last release.

[codecov]

Codecov Report

Attention: Patch coverage is 89.15663% with 9 lines in your changes missing coverage. Please review.

Project coverage is 91.29%. Comparing base (5f95f72) to head (dfa9a23).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
exporter/exporterhelper/internal/base_exporter.go	94.44%	2 Missing and 1 partial ⚠️
exporter/exporterhelper/internal/queue_sender.go	72.72%	2 Missing and 1 partial ⚠️
exporter/exporterhelper/internal/request_sender.go	40.00%	2 Missing and 1 partial ⚠️

❌ Your patch status has failed because the patch coverage (89.15%) is below the target coverage (95.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #12239      +/-   ##
==========================================
- Coverage   91.31%   91.29%   -0.03%     
==========================================
  Files         465      465              
  Lines       25654    25662       +8     
==========================================
+ Hits        23427    23429       +2     
- Misses       1814     1818       +4     
- Partials      413      415       +2     

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[dmitryax]

LGTM. Thanks for the fix!