Add default index settings when parsing index

[jmazanec15]

Issue #, if available:
#204

Description of changes:
Adds in default settings if an exception is thrown when attempting to get settings for the index during parsing. More details on why this is needed in the issue.

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[codecov]

Codecov Report

Merging #205 into master will increase coverage by 0.51%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #205      +/-   ##
============================================
+ Coverage     76.44%   76.95%   +0.51%     
- Complexity      301      302       +1     
============================================
  Files            50       50              
  Lines          1163     1189      +26     
  Branches        100      100              
============================================
+ Hits            889      915      +26     
  Misses          225      225              
  Partials         49       49              

Impacted Files	Coverage Δ	Complexity Δ
...ndistroforelasticsearch/knn/index/KNNSettings.java	83.47% <100.00%> (+1.48%)	27.00 <0.00> (ø)
...relasticsearch/knn/index/KNNVectorFieldMapper.java	77.85% <100.00%> (+2.85%)	15.00 <1.00> (+1.00)

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[vamshin]

LGTM! Thanks for the fix