add comparison workflow example

[pmeier]

Addresses #18. This shows two things:

1. How to compare multiple components with each other.
2. How to effectively use async programming to speed this up.

I don't intend to merge this PR as we need to have something like that as part of our documentation. But it can serve as base for future work.

@nenb You might also be able to use this for the comparisons you wanted to do in #205 (comment).

Here is the progress bar output on my machine:

100%|█████████████████████████████████████████████████████████████████████████| 4/4 [00:38<00:00,  9.61s/it]
100%|█████████████████████████████████████████████████████████████████████████| 4/4 [00:17<00:00,  4.31s/it]

So we are roughly twice as fast with utilizing async. This of course will vary a lot for different source storages / assistants / documents / prompts. So we cannot ever report a number here unless we create a fixed test scenario first.