Update license headers (Backport 194)

[jmazanec15]

Description

Backport #194

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[codecov-commenter]

Codecov Report

Merging #195 (adaa461) into 1.2 (2fb004f) will increase coverage by 0.02%.
The diff coverage is n/a.

❗ Current head adaa461 differs from pull request most recent head cdea57b. Consider uploading reports for the commit cdea57b to get more accurate results

@@             Coverage Diff              @@
##                1.2     #195      +/-   ##
============================================
+ Coverage     83.05%   83.08%   +0.02%     
- Complexity      857      858       +1     
============================================
  Files           123      123              
  Lines          3759     3759              
  Branches        359      359              
============================================
+ Hits           3122     3123       +1     
+ Misses          476      475       -1     
  Partials        161      161              

Impacted Files	Coverage Δ
...n/java/org/opensearch/knn/common/KNNConstants.java	92.30% <ø> (ø)
...n/common/exception/KNNInvalidIndicesException.java	80.00% <ø> (ø)
...va/org/opensearch/knn/index/KNNCircuitBreaker.java	60.00% <ø> (ø)
...n/java/org/opensearch/knn/index/KNNIndexShard.java	92.85% <ø> (ø)
...c/main/java/org/opensearch/knn/index/KNNQuery.java	77.77% <ø> (+5.55%)	⬆️
...java/org/opensearch/knn/index/KNNQueryBuilder.java	67.96% <ø> (ø)
.../java/org/opensearch/knn/index/KNNQueryResult.java	100.00% <ø> (ø)
.../main/java/org/opensearch/knn/index/KNNScorer.java	64.28% <ø> (ø)
...ain/java/org/opensearch/knn/index/KNNSettings.java	81.75% <ø> (ø)
...opensearch/knn/index/KNNVectorDVLeafFieldData.java	72.72% <ø> (ø)
... and 48 more

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[vamshin]

LGTM! Thanks