Add GremlinGraph and GremlinQAChain in langchainjs

[keiohtani]

Checked

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Feature request

I would like to LangChainJs to support Gremlin like the Python counterpart. For my own project, I ended up implementing the classes on my own mimicking the Python implementation and I have the working code. I am happy to open a PR for this if this is not already work in progress.

Motivation

LangChain Python already supports this feature, and I believe we should bring this to JS as well. Here is the link to the Python Gremlin page. https://python.langchain.com/docs/integrations/graphs/azure_cosmosdb_gremlin/

Proposal (If applicable)

No response