actionify delete policy API

[bowenlan-amzn]

Issue #, if available:
#292

Description of changes:
actionify delete 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 #308 into master will increase coverage by 0.09%.
The diff coverage is 74.28%.

@@             Coverage Diff              @@
##             master     #308      +/-   ##
============================================
+ Coverage     75.36%   75.45%   +0.09%     
- Complexity      852      861       +9     
============================================
  Files           120      123       +3     
  Lines          4506     4535      +29     
  Branches        674      677       +3     
============================================
+ Hits           3396     3422      +26     
+ Misses          747      742       -5     
- Partials        363      371       +8     

Impacted Files	Coverage Δ	Complexity Δ
...temanagement/resthandler/RestDeletePolicyAction.kt	81.81% <60.00%> (-18.19%)	4.00 <1.00> (ø)
...ransport/action/deletepolicy/DeletePolicyAction.kt	66.66% <66.66%> (ø)	2.00 <2.00> (?)
...action/deletepolicy/TransportDeletePolicyAction.kt	71.42% <71.42%> (ø)	2.00 <2.00> (?)
...ansport/action/deletepolicy/DeletePolicyRequest.kt	76.47% <76.47%> (ø)	6.00 <6.00> (?)
...ticsearch/indexmanagement/IndexManagementPlugin.kt	91.66% <100.00%> (+0.11%)	9.00 <0.00> (ø)
.../transport/action/indexpolicy/IndexPolicyAction.kt	66.66% <100.00%> (ø)	2.00 <0.00> (ø)
...nt/indexstatemanagement/model/destination/Slack.kt	40.90% <0.00%> (-13.64%)	2.00% <0.00%> (-2.00%)
...icsearch/indexmanagement/IndexManagementIndices.kt	64.91% <0.00%> (-5.27%)	10.00% <0.00%> (ø%)
...anagement/indexstatemanagement/model/Transition.kt	63.07% <0.00%> (-4.62%)	5.00% <0.00%> (ø%)
...dexstatemanagement/elasticapi/ElasticExtensions.kt	61.53% <0.00%> (-3.85%)	0.00% <0.00%> (ø%)
... and 5 more

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