Add optional id_field to VertexRank

[shenghann]

There are valid use cases to retain the id field in the original retrieved documents in the documents that are reranked by VertexRank. This is especially important for use cases where traceability of documents throughout the chain is important.

Current assigned id based on an enumerated incrementing index works for cases where ids do not need to be tracked but isn't universally applicable.

[gmogr]

/gcbrun

[lkuligin]

@shenghann linter is red

[lkuligin]

@shenghann you can run linter locally with make format and make lint commands https://github.com/langchain-ai/langchain-google/blob/main/libs/community/Makefile