docs: Improve automated documentation generation

[charlieegan3]

Regal's docs content is good, but the process by which it is rendered into the docs.styra.com/regal site is showing cracks. In addition, we need to have a better way to showcase Rules as we now have a large number of them. This is something we need to make sure is solid for v1.

[charlieegan3]

We now have a searchable rules table at https://docs.styra.com/regal/rules and on category pages: e.g. https://docs.styra.com/regal/rules/bugs

In addition, we have an index page https://docs.styra.com/regal generated from sections which is shared with the readme on GH.

Pages are only copied to the site when they have a yaml metadata sidecar file in docs: https://github.com/StyraInc/regal/tree/main/docs