feat: render readthedocs flyout menu for default theme

[jkowalleck]

Template issue/request

Search Terms

• readthedocs
• rtfd
• readthedocs-embed-flyout

Problem

When rendering the docs and publishing them to https://readthedocs.com
I don't have usual "flyout menu" visible, or it is rendered incorrectly.

read the details here: https://docs.readthedocs.io/en/stable/flyout-menu.html

dummy project:

• https://github.com/jkowalleck/testing_rtfd/tree/push-prerendered
• rendered as https://jkowalleck-testing-rtfd.readthedocs.io/en/push-prerendered/

Suggested Solution

Add the needed functionality and styling to the default theme, so the readthedocs menu may be rendered.
Maybe hide the functionality behind an environment variable READTHEDOCS -- see https://docs.readthedocs.io/en/stable/reference/environment-variables.html#environment-variable-reference