Use autosummary for interfaces, functions, and pointfree docs

[sobolevn]

We need to add .. autosummary:: to pages that need it.
We also need to make sure that this tag renders smoothly.

Usage example: https://github.com/wemake-services/wemake-python-styleguide/blob/ba060dfd18606365d4c09545554b595fce025e79/wemake_python_styleguide/violations/best_practices.py#L16-L17
Docs: https://www.sphinx-doc.org/en/master/usage/extensions/autosummary.html