Simplify OpenSearchIndexScanBuilder (#275)

[MaxKsyunz]

Refactoring OpenSearchIndexScanBuilder to address feedback from pagination PR.

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[codecov]

Codecov Report

Merging #1738 (2464d55) into main (bd9b180) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 2464d55 differs from pull request most recent head d69b144. Consider uploading reports for the commit d69b144 to get more accurate results

@@            Coverage Diff            @@
##               main    #1738   +/-   ##
=========================================
  Coverage     97.30%   97.30%           
- Complexity     4326     4329    +3     
=========================================
  Files           385      385           
  Lines         10807    10811    +4     
  Branches        762      762           
=========================================
+ Hits          10516    10520    +4     
  Misses          284      284           
  Partials          7        7           

Flag	Coverage Δ
sql-engine	97.30% <100.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
...search/sql/opensearch/storage/OpenSearchIndex.java	100.00% <100.00%> (ø)
...earch/storage/scan/OpenSearchIndexScanBuilder.java	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes