Adds rollup search service which handles aggregating the results from…

[dbbaughe]

… the source index

Issue #, if available:

Description of changes:
This is missing the associated integ tests as they are written with the runner logic existing in mind. They will be included in the PR that contains the rollup runner logic.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

Merging #338 (0a6fb1c) into master (24be8b7) will decrease coverage by 1.30%.
The diff coverage is 2.85%.

@@             Coverage Diff              @@
##             master     #338      +/-   ##
============================================
- Coverage     74.31%   73.01%   -1.31%     
  Complexity     1187     1187              
============================================
  Files           180      181       +1     
  Lines          5973     6078     +105     
  Branches        899      921      +22     
============================================
- Hits           4439     4438       -1     
- Misses         1072     1174     +102     
- Partials        462      466       +4     

Impacted Files	Coverage Δ	Complexity Δ
...csearch/indexmanagement/rollup/util/RollupUtils.kt	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...arch/indexmanagement/rollup/RollupSearchService.kt	10.00% <6.38%> (-56.67%)	1.00 <0.00> (ø)
...icsearch/indexmanagement/IndexManagementIndices.kt	62.06% <0.00%> (-3.45%)	10.00% <0.00%> (ø%)
...anagement/indexstatemanagement/model/Transition.kt	64.61% <0.00%> (-3.08%)	5.00% <0.00%> (ø%)
...ndexstatemanagement/IndexStateManagementHistory.kt	75.96% <0.00%> (-1.93%)	27.00% <0.00%> (-1.00%)
...ent/rollup/action/explain/ExplainRollupResponse.kt	80.00% <0.00%> (+10.00%)	6.00% <0.00%> (+1.00%)

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