Added support for asynchronous processing for chat

[m-messer]

Summary

Added a callBackUrl option for chat, aligning with the current EvaluateRequest design.
The callback could be used for returning intermediate reasoning steps to the the user.

Related issue

#36

Scope

• This pull request is focused on a single concern.
• The change was started from the latest main branch, or from a fork if direct branch creation is not available.

Validation

• npm run lint
• npm run bundle

[neagualexa]

I am a bit confused, so is the callback url called first for resolving immediate steps before the main service provides the final response? or you could access the intermediate reasoning steps by going to the callback url?
Should we not also adopt the response body to allow for return of immediate steps?

[m-messer]

So from my understanding of how I have implemented the callback for evalute:

1. LF calls the microservice with callback URL
2. Microservice sends feedback to that callback URL
3. Microservice finishes, and return value and/or the microserivce sends the final response

[maximiliansoelch]

Just two minor suggestions so this better fits for chat.
But as this is only an example and the description, the PR can also be merged like this.

[maximiliansoelch]

@neagualexa Regarding your question:
A callbackUrl is normally called once at the end of processing with the final result. For longer-running tasks, this allows the service requesting feedback or chat results to immediately close the initial request and continue with other tasks.

Regarding your intermediate steps, e.g., returning reasoning to the caller, etc.: This would be part of the normal response. Alternatively, you could think about if it is required to open an additional streaming channel/connection after the normal request.