Implement chat_history for openai_functions_agent

[masrad]

Adds chat_history memory to openai_functions agent so that the agent takes chat_history into account when formulating responses

Who can review?

Tag maintainers/contributors who might be interested:

@hwchase17 @dev2049

[0ptim]

Possible duplicate of #6165. I think you are doing the same thing, but a little different. But yours is for a more up-to-date master.

[masrad]

Possible duplicate of #6165. I think you are doing the same thing, but a little different. But yours is for a more up-to-date master.

Thank you, good call I hadn't seen that one. Also looks like while their implementation is based off of how StructuredChatAgent implements memory, I had based mine off of how the ConversationalChatAgent handles chat history

[hwchase17]

we'll support memory with the other pr