Add an Action to Setting Index Priority

[bowenlan-amzn]

Issue #, if available:
#142

Description of changes:

possible use case

Sets the priority of the index as soon as the policy enters certain state. Unallocated shards of indices are recovered in order of priority, whenever possible.
reference from ES

"actions": [
    {
        "index_priority": {
            "priority": 50
        }
    }
]

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 #241 into master will increase coverage by 0.42%.
The diff coverage is 78.46%.

@@             Coverage Diff              @@
##             master     #241      +/-   ##
============================================
+ Coverage     70.84%   71.27%   +0.42%     
- Complexity      613      625      +12     
============================================
  Files            83       86       +3     
  Lines          3584     3648      +64     
  Branches        593      601       +8     
============================================
+ Hits           2539     2600      +61     
+ Misses          742      737       -5     
- Partials        303      311       +8     

Impacted Files	Coverage Δ	Complexity Δ
.../indexstatemanagement/model/action/ActionConfig.kt	93.75% <66.66%> (+0.27%)	8.00 <0.00> (ø)
...nagement/model/action/IndexPriorityActionConfig.kt	69.56% <69.56%> (ø)	4.00 <4.00> (?)
...indexstatemanagement/action/IndexPriorityAction.kt	83.33% <83.33%> (ø)	2.00 <2.00> (?)
.../step/indexpriority/AttemptSetIndexPriorityStep.kt	84.84% <84.84%> (ø)	4.00 <4.00> (?)
...ticsearch/indexstatemanagement/model/Transition.kt	80.39% <0.00%> (ø)	5.00% <0.00%> (ø%)
...exstatemanagement/model/destination/Destination.kt	47.05% <0.00%> (+1.47%)	6.00% <0.00%> (+1.00%)
...ch/indexstatemanagement/model/destination/Chime.kt	57.14% <0.00%> (+42.85%)	4.00% <0.00%> (+1.00%)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b4ab545...f931b0f. Read the comment docs.

[bowenlan-amzn]

already checked this has no conflict with opendistro-1.9 update, safe to merge in

[qreshi]

NP: Missing newlines in between function definitions