Allow async pipe

[dominikpeter]

fixes #411
fixes #359

[gdbb]

Awesome! I reviewd some pipeline demo for old version openwebui, and there are async pipe and many parameters like event_emitter. I'm curious why all of these are removed.

[dominikpeter]

Aren't these Pipe functions?

Like this example I found:
Example

But yes, having event_emitter in the pipelines would also be great. We use it for RAG and being able to give feedback to the user would be great. We might have to create another issue for that.

The async pipe here should not break the existing code, as it just adds the option to use async, which should work as before for sync. But the repos has no tests that I can really test it. It may have some side effects I am not aware of. However, we have run this on our fork already and had no problems so far.

We can now use langchain in this way without having to rewrite our existing code:

async for chunk in model.astream("hello. tell me something about yourself"):
    yield chunk

[tjbck]

You use should the same approach Open WebUI uses and keep the changes to our core codebase minimal, changes wanted here.

[maximegmd]

Is there a reason why this was not merged?

[dominikpeter]

I can resolve the conflicts or refactor it if nothing is fundamentally wrong and has a chance of being merged. Just let me know.