Updating license headers

[downsrob]

Signed-off-by: Robert Downs downsrob@amazon.com

Issue #, if available:
#114

Description of changes:
Corrects the copyright license header as per the linked issue requirements. Besides the gradlew file, which maintained the same copyright as an external file, the short form was used for all files, as I didn't notice any others with an attribution to an external project.

CheckList:

• Commits are signed 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 #196 (512c408) into main (1fe36be) will decrease coverage by 0.20%.
The diff coverage is n/a.

❗ Current head 512c408 differs from pull request most recent head 0e3361e. Consider uploading reports for the commit 0e3361e to get more accurate results

@@             Coverage Diff              @@
##               main     #196      +/-   ##
============================================
- Coverage     75.69%   75.49%   -0.21%     
+ Complexity     1926     1920       -6     
============================================
  Files           260      260              
  Lines         11094    11094              
  Branches       1746     1746              
============================================
- Hits           8398     8375      -23     
- Misses         1755     1774      +19     
- Partials        941      945       +4     

Impacted Files	Coverage Δ
...ensearch/indexmanagement/IndexManagementIndices.kt	60.71% <ø> (ø)
...pensearch/indexmanagement/IndexManagementPlugin.kt	92.71% <ø> (ø)
...pensearch/indexmanagement/IndexManagementRunner.kt	55.55% <ø> (ø)
...management/common/model/dimension/DateHistogram.kt	75.60% <ø> (ø)
...ndexmanagement/common/model/dimension/Dimension.kt	85.71% <ø> (ø)
...ndexmanagement/common/model/dimension/Histogram.kt	65.07% <ø> (ø)
...ch/indexmanagement/common/model/dimension/Terms.kt	77.04% <ø> (ø)
...agement/indexstatemanagement/ISMTemplateService.kt	79.54% <ø> (ø)
...ndexstatemanagement/IndexStateManagementHistory.kt	80.14% <ø> (ø)
...nt/indexstatemanagement/ManagedIndexCoordinator.kt	71.77% <ø> (ø)
... and 259 more

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[bowenlan-amzn]

Great!