actionify index policy action

[bowenlan-amzn]

Issue #, if available:
#292

Description of changes:
actionify index policy API, refactor our API code so we have an action name to each API

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 #305 into master will decrease coverage by 0.26%.
The diff coverage is 73.28%.

@@             Coverage Diff              @@
##             master     #305      +/-   ##
============================================
- Coverage     75.14%   74.87%   -0.27%     
- Complexity      788      829      +41     
============================================
  Files           112      116       +4     
  Lines          4200     4442     +242     
  Branches        645      670      +25     
============================================
+ Hits           3156     3326     +170     
- Misses          702      753      +51     
- Partials        342      363      +21     

Impacted Files	Coverage Δ	Complexity Δ
...nt/indexstatemanagement/model/ErrorNotification.kt	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
...anagement/indexstatemanagement/model/Transition.kt	64.61% <0.00%> (-17.74%)	5.00 <0.00> (ø)
...statemanagement/model/destination/CustomWebhook.kt	65.21% <0.00%> (-26.62%)	12.00 <0.00> (ø)
...nt/indexstatemanagement/model/destination/Chime.kt	40.90% <50.00%> (-16.24%)	2.00 <1.00> (-2.00)
...t/action/indexpolicy/TransportIndexPolicyAction.kt	65.95% <65.95%> (ø)	3.00 <3.00> (?)
...exstatemanagement/model/destination/Destination.kt	50.64% <66.66%> (+2.11%)	9.00 <2.00> (+2.00)
.../transport/action/indexpolicy/IndexPolicyAction.kt	66.66% <66.66%> (ø)	2.00 <2.00> (?)
.../indexstatemanagement/model/action/ActionConfig.kt	85.33% <68.00%> (-8.67%)	9.00 <1.00> (+1.00)	⬇️
...atemanagement/resthandler/RestIndexPolicyAction.kt	94.44% <71.42%> (+10.15%)	8.00 <0.00> (ø)
...nt/indexstatemanagement/model/destination/Slack.kt	54.54% <83.33%> (-2.60%)	4.00 <3.00> (ø)
... and 21 more

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