[Backport 2.x] GetIndexMappings index pattern support

[opensearch-trigger-bot]

Backport 0dbbbfc from #265

[codecov-commenter]

Codecov Report

Merging #275 (a9edd49) into 2.x (3e8b089) will increase coverage by 0.26%.
The diff coverage is 69.38%.

@@             Coverage Diff              @@
##                2.x     #275      +/-   ##
============================================
+ Coverage     36.88%   37.15%   +0.26%     
- Complexity      882      887       +5     
============================================
  Files           179      179              
  Lines          6948     6973      +25     
  Branches        845      849       +4     
============================================
+ Hits           2563     2591      +28     
+ Misses         4149     4145       -4     
- Partials        236      237       +1     

Impacted Files	Coverage Δ
...search/securityanalytics/mapper/MapperService.java	4.54% <0.00%> (+0.08%)	⬆️
...ics/transport/TransportGetIndexMappingsAction.java	0.00% <ø> (ø)
...ch/securityanalytics/mapper/MappingsTraverser.java	82.35% <89.47%> (-0.70%)	⬇️

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