[Backport 2.x] [FIX] Failed concurrent creates of ISM policies should return http 409

[opensearch-trigger-bot]

Backport 2f7d009 from #461

[codecov-commenter]

Codecov Report

Merging #464 (ec4a43a) into 2.x (4811922) will decrease coverage by 0.12%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##                2.x     #464      +/-   ##
============================================
- Coverage     75.96%   75.83%   -0.13%     
+ Complexity     2475     2474       -1     
============================================
  Files           314      314              
  Lines         14440    14442       +2     
  Branches       2233     2234       +1     
============================================
- Hits          10969    10952      -17     
- Misses         2224     2240      +16     
- Partials       1247     1250       +3     

Impacted Files	Coverage Δ
...t/action/indexpolicy/TransportIndexPolicyAction.kt	79.09% <0.00%> (-1.47%)	⬇️
...statemanagement/model/destination/CustomWebhook.kt	67.14% <0.00%> (-28.58%)	⬇️
.../rollup/action/start/TransportStartRollupAction.kt	72.94% <0.00%> (-2.36%)	⬇️
...gement/indexstatemanagement/action/ShrinkAction.kt	70.58% <0.00%> (-1.48%)	⬇️
...ndexstatemanagement/IndexStateManagementHistory.kt	78.62% <0.00%> (-1.38%)	⬇️
...earch/indexmanagement/transform/TransformRunner.kt	78.01% <0.00%> (-0.71%)	⬇️
.../opensearch/indexmanagement/rollup/model/Rollup.kt	85.58% <0.00%> (-0.47%)	⬇️
...earch/indexmanagement/transform/model/Transform.kt	85.47% <0.00%> (-0.43%)	⬇️
...nt/indexstatemanagement/ManagedIndexCoordinator.kt	69.29% <0.00%> (ø)
...nt/rollup/action/stop/TransportStopRollupAction.kt	77.64% <0.00%> (ø)
... and 3 more

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