Add more group headers to the plugin hooks page

Currently: https://docs.datasette.io/en/latest/plugin_hooks.html

![Screen Shot 2024-03-12 at 15 43 09](https://github.com/simonw/datasette/assets/9599/5cff5293-b2df-4931-b345-4266a479f5fa)

I'm going to group the page extras and action menu sections too.