Introduce batching support for embedding documents

[sobychacko]

Introduce a way for EmbeddingModel implementations to embed Document objects using a batching strategy.

[sobychacko]

Using this #1140 as a starting point, introduce a new API for batching for all vector stores and embedding models to use.

[impactCn]

@sobychacko hi, I also encountered the same problem in PG. The segmentation process I use , #1200 .
Can you guide me on how to use this batch API?

[sobychacko]

@impactCn Sorry for the delay in responding. We just merged similar batching changes for the PG vector store. Can you take a look and see if that satisfies your use case? If there is a gap, we can improve on that. Thanks!