Automate and schedule the pylab-render github action

[shirlywhirl]

The action should run

poetry install
poetry run python embed.py skip_embed ${SHIRLYWHIRLMD}

Then commit the changes into shirlywhirlmd and pushing them in main will trigger the rebuild of the site. Once per week is ideal

This line will certainly have to change: https://github.com/shirlywhirl/pylab/blob/main/post.py#L40 its a dumb hardcode. Github actions will likely have an environment variable to utilize for this, but also ../shirlywhirlmd is likely to just work.

Ensure the action does not leak the github secret!