[WIP] BatchElements Transform for Java SDK

[Ganeshsivakumar]

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Summary of Changes

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This pull request introduces a new PTransform called BatchElements to the Apache Beam Java SDK. The purpose of this transform is to facilitate the grouping of elements within a PCollection into lists, enabling efficient batch processing. The implementation includes a mechanism for estimating batch sizes based on performance metrics.

Highlights

• New Transform Implementation: Introduced the BatchElements PTransform to the Java SDK, which is designed to group elements into batches.
• Batch Size Estimation: Added a BatchSizeEstimator inner class to track processing time and dynamically determine optimal batch sizes.

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