Update build.gradle to build main jar

[khushbr]

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Update build.gradle to build main jar. Missing Main JAR is causing failure when publishing the JAR to Maven Central

Test:

% ls /Users/khushbr/.m2/repository/org/opensearch/performance-analyzer-commons/1.0.0
performance-analyzer-commons-1.0.0-javadoc.jar	performance-analyzer-commons-1.0.0.jar		performance-analyzer-commons-1.0.0.pom
performance-analyzer-commons-1.0.0-sources.jar	performance-analyzer-commons-1.0.0.module

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

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