Adds settings for rollup feature

[dbbaughe]

Issue #, if available:

Description of changes:

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 #323 (6b3ae19) into master (f173dbe) will increase coverage by 0.45%.
The diff coverage is 97.72%.

@@             Coverage Diff              @@
##             master     #323      +/-   ##
============================================
+ Coverage     73.76%   74.22%   +0.45%     
  Complexity     1169     1169              
============================================
  Files           173      174       +1     
  Lines          5894     5937      +43     
  Branches        898      898              
============================================
+ Hits           4348     4407      +59     
+ Misses         1081     1065      -16     
  Partials        465      465              

Impacted Files	Coverage Δ	Complexity Δ
.../indexmanagement/rollup/settings/RollupSettings.kt	97.22% <97.22%> (ø)	1.00 <1.00> (?)
...ticsearch/indexmanagement/IndexManagementPlugin.kt	91.66% <100.00%> (+0.65%)	9.00 <0.00> (ø)
...nt/indexstatemanagement/model/destination/Chime.kt	40.90% <0.00%> (-13.64%)	2.00% <0.00%> (-2.00%)
...dexstatemanagement/elasticapi/ElasticExtensions.kt	65.11% <0.00%> (-2.33%)	0.00% <0.00%> (ø%)
...ndexstatemanagement/IndexStateManagementHistory.kt	75.96% <0.00%> (-1.93%)	27.00% <0.00%> (-1.00%)
...anagement/indexstatemanagement/model/Transition.kt	67.69% <0.00%> (+4.61%)	5.00% <0.00%> (ø%)
...statemanagement/model/destination/CustomWebhook.kt	94.20% <0.00%> (+28.98%)	14.00% <0.00%> (+2.00%)

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