[ML] Add rerank chunking for elastic reranker

[dan-rubinstein]

This issue is to track adding recursive chunking to the elastic reranker. This would allow users to opt into using chunking instead of truncating and would allow them to configure how many chunks are generated per document to send to the elastic reranker model.

[elasticsearchmachine]

Pinging @elastic/ml-core (Team:ML)

[dan-rubinstein]

Added as part of #130485