Scaffold cookbook recipes

I would like to replicate [Servant's cookbook recipes](https://docs.servant.dev/en/0.20.3.0/cookbook/index.html) to help people writing Beam-based software.

The idea would be to have SQL queries and their matching Beam implementation. [This is how Rel8 does it](https://rel8.readthedocs.io/en/latest/cookbook.html), for example.

This issue should be considered completed when there's a well-defined process to include recipes in the cookbook, such that people can easily contribute recipes.