Runnable that takes inputs and produces a string output.
The inputs to this will be any original inputs to this chain, a new
context key with the retrieved documents, and chat_history (if not present
in the inputs) with a value of [] (to easily enable conversational
retrieval).
Retriever-like object that returns list of documents. Should
either be a subclass of BaseRetriever or a Runnable that returns
a list of documents. If a subclass of BaseRetriever, then it
is expected that an input key be passed in - this is what
is will be used to pass into the retriever. If this is NOT a
subclass of BaseRetriever, then all the inputs will be passed
into this runnable, meaning that runnable should take a object
as input.
Parameters for the createRetrievalChain method.