actionify explain API

[bowenlan-amzn]

Issue #, if available:
#292

Description of changes:
actionify explain 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 #304 into master will increase coverage by 0.23%.
The diff coverage is 92.50%.

@@             Coverage Diff              @@
##             master     #304      +/-   ##
============================================
+ Coverage     74.90%   75.14%   +0.23%     
- Complexity      769      787      +18     
============================================
  Files           108      112       +4     
  Lines          4145     4200      +55     
  Branches        642      645       +3     
============================================
+ Hits           3105     3156      +51     
- Misses          700      702       +2     
- Partials        340      342       +2     

Impacted Files	Coverage Δ	Complexity Δ
...nagement/transport/action/explain/ExplainAction.kt	66.66% <66.66%> (ø)	2.00 <2.00> (?)
...agement/transport/action/explain/ExplainRequest.kt	89.47% <89.47%> (ø)	7.00 <7.00> (?)
...transport/action/explain/TransportExplainAction.kt	90.32% <90.32%> (ø)	2.00 <2.00> (?)
...ticsearch/indexmanagement/IndexManagementPlugin.kt	91.30% <100.00%> (+0.12%)	9.00 <0.00> (ø)
...exstatemanagement/resthandler/RestExplainAction.kt	91.66% <100.00%> (-5.31%)	6.00 <0.00> (-1.00)
...gement/transport/action/explain/ExplainResponse.kt	100.00% <100.00%> (ø)	8.00 <8.00> (?)
...anagement/indexstatemanagement/model/Transition.kt	82.35% <0.00%> (-3.93%)	5.00% <0.00%> (ø%)
...ndexstatemanagement/IndexStateManagementHistory.kt	75.96% <0.00%> (-1.93%)	27.00% <0.00%> (-1.00%)
... and 4 more

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[dbbaughe]

Remove wildcard import