Update license headers

[naveentatikonda]

Description

• Removed Amazon License Header in all files listed here
• Updated NOTICE and CONTRIBUTING.md as per copyright policies
• Replaced Apache License Header with short version in all files listed here

Issues Resolved

#193

Check List

• Commits are signed as per the DCO using --signoff

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 #194 (3aea1c7) into main (5fcd818) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##               main     #194   +/-   ##
=========================================
  Coverage     83.08%   83.08%           
  Complexity      858      858           
=========================================
  Files           123      123           
  Lines          3759     3759           
  Branches        359      359           
=========================================
  Hits           3123     3123           
  Misses          475      475           
  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> (ø)
...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 47 more

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[vamshin]

LGTM! Thanks