[Feature Request]: Implement BatchElements in the beam-java-sdk

[RustedBones]

What would you like to happen?

Beam's python SDK supports BatchElements that batches elements without having to be keyed like in GroupIntoBatches

This API is not available in the Java SDK but may be helpful, eg. to issue batch requests to external services over the network when there are no limitations on the maximum number of connections

Issue Priority

Priority: 3

Issue Component

Component: sdk-java-core

[lucasfehres-cloudwise]

This has been implemented (and merged) in #38369.