Components expecting List[...] input should use Iterable[...] instead

[bendavis78]

For example, let's say I have a generator that yields my documents:

def get_documents():
    for some_thing in some_other_generator():
        yield some_thing

In order to use the OpenAIDocumentEmbedder with this, I get this error I am forced to exhaust the python generator and load all documents into memory.

Many components in the haystack library require List when an Iterable would do just fine. For example, OpenAIDocumentEmbedder could be updated to use pyhthon generators instead of raw lists, making the process more memory effecitent.