Follow up to/extension of elixir-lang#13173

First draft, happy to adjust and extend it in many ways. I had
trouble coming up with a simple example as we needed a bunch of
data to make sure it's not good. I could have employed the first
anti pattern myself and did repeated statistics calculation, but
that'd have been worse :sweat-smile:

I remembered José's comment around sending along the `conn` and
figured it's central enough in elixir to not throw anyone off.

If someone has a better example, happy to redo it!

Thanks y'all! :green-heart:

Excellent suggestions and improvements on wording from @Netzteb!

Co-authored-by: Noah Betzen <noah@nezteb.net>

And @whatyouhide also came in with a round of improvements, thank you!

Co-authored-by: Andrea Leopardi <an.leopardi@gmail.com>