[Backport 2.x] update put route when flattening result index

[opensearch-trigger-bot]

Backport d4ce6cf from #1409.

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 5 lines in your changes missing coverage. Please review.

Project coverage is 81.65%. Comparing base (328f901) to head (303bd5f).
Report is 1 commits behind head on 2.x.

Files with missing lines	Patch %	Lines
.../rest/handler/AbstractTimeSeriesActionHandler.java	80.00%	3 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x    #1410      +/-   ##
============================================
- Coverage     81.69%   81.65%   -0.05%     
+ Complexity     5879     5871       -8     
============================================
  Files           533      533              
  Lines         23676    23665      -11     
  Branches       2375     2374       -1     
============================================
- Hits          19343    19323      -20     
- Misses         3178     3183       +5     
- Partials       1155     1159       +4     

Flag	Coverage Δ
plugin	81.65% <80.00%> (-0.05%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...g/opensearch/timeseries/util/RestHandlerUtils.java	67.46% <ø> (+3.64%)	⬆️
.../rest/handler/AbstractTimeSeriesActionHandler.java	93.07% <80.00%> (-0.20%)	⬇️

... and 9 files with indirect coverage changes