Refactors shrink action steps and adds unit tests

[downsrob]

Issue #, if available:
#40

Description of changes:
Adds additional unit tests for the shrink action step util functions and refactors the shrink action steps for readability and reduced code duplication. Also fixes a bug where the shrink action would not wait for a copy of each shard to move to the selected node before initiating the shrink.

CheckList:

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[codecov-commenter]

Codecov Report

Merging #349 (acb07d4) into main (a7fd6c4) will increase coverage by 0.20%.
The diff coverage is 47.36%.

@@             Coverage Diff              @@
##               main     #349      +/-   ##
============================================
+ Coverage     75.09%   75.30%   +0.20%     
- Complexity     2135     2155      +20     
============================================
  Files           262      263       +1     
  Lines         12444    12413      -31     
  Branches       1966     1974       +8     
============================================
+ Hits           9345     9347       +2     
+ Misses         2028     1984      -44     
- Partials       1071     1082      +11     

Impacted Files	Coverage Δ
...exstatemanagement/step/shrink/AttemptShrinkStep.kt	60.71% <33.33%> (+10.20%)	⬆️
...ent/indexstatemanagement/step/shrink/ShrinkStep.kt	36.26% <36.26%> (ø)
...exstatemanagement/step/shrink/WaitForShrinkStep.kt	42.00% <36.36%> (+10.42%)	⬆️
...atemanagement/step/shrink/WaitForMoveShardsStep.kt	49.23% <55.81%> (+12.27%)	⬆️
...atemanagement/step/shrink/AttemptMoveShardsStep.kt	60.42% <64.81%> (+4.87%)	⬆️
...xmanagement/indexstatemanagement/util/StepUtils.kt	87.64% <100.00%> (+6.99%)	⬆️
...nt/indexstatemanagement/ManagedIndexCoordinator.kt	68.71% <0.00%> (-6.52%)	⬇️
...arch/indexmanagement/rollup/RollupSearchService.kt	57.40% <0.00%> (-3.71%)	⬇️
...ent/indexstatemanagement/util/ManagedIndexUtils.kt	76.10% <0.00%> (-0.24%)	⬇️
... and 6 more

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