Updated copyright headers for Root project, API, and Core

[dlvenable]

Description

Updates to copyright headers to parts of the project:

• Gradle files in root directory
• data-prepper-api
• data-prepper-core

Issues Resolved

Part of #189

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• 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 #569 (565c87e) into main (90f3427) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##               main     #569   +/-   ##
=========================================
  Coverage     92.28%   92.28%           
  Complexity      569      569           
=========================================
  Files            71       71           
  Lines          1725     1725           
  Branches        144      144           
=========================================
  Hits           1592     1592           
  Misses          102      102           
  Partials         31       31           

Impacted Files	Coverage Δ
.../com/amazon/dataprepper/metrics/PluginMetrics.java	100.00% <ø> (ø)
.../com/amazon/dataprepper/model/CheckpointState.java	100.00% <ø> (ø)
.../java/com/amazon/dataprepper/model/PluginType.java	100.00% <ø> (ø)
...mazon/dataprepper/model/buffer/AbstractBuffer.java	100.00% <ø> (ø)
...ataprepper/model/buffer/SizeOverflowException.java	100.00% <ø> (ø)
...dataprepper/model/configuration/PipelineModel.java	100.00% <ø> (ø)
...n/dataprepper/model/configuration/PluginModel.java	100.00% <ø> (ø)
...dataprepper/model/configuration/PluginSetting.java	100.00% <ø> (ø)
.../dataprepper/model/event/DefaultEventMetadata.java	100.00% <ø> (ø)
.../com/amazon/dataprepper/model/event/EventType.java	100.00% <ø> (ø)
... and 43 more

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