Improve docs on Caching

[shoooe]

📋 Explain your issue

A common document page in other frameworks is caching. Since SolidJS just uses Nitro, caching can be easily implemented via the routeRules setting as described here: https://stackoverflow.com/q/79223996/493122

Would this be worth adding to the docs?

[brenelz]

Could maybe add a note here https://docs.solidjs.com/solid-start/reference/config/define-config, but I'm sure where the docs stand on nitro specific things when you could just look at things over there

[atilafassina]

Yeah, we try not to document Nitro directly (because it's a slippery slope, soon we end up documenting H3, Vite, etc...) - but I believe a note to that would be helpful.

We could also add a Caching section to our Learn guide for start where we explain our deduplication system and how to leverage Nitro caching, and how to play with HTTP headers for Max-Age, SWR, etc on Server Functions (tapping into the request event and so on) - that would be super useful.

suggested action items

• Add a explicit note about caching on the "configuring Nitro" section
• Create a section on how to handle cache within Server Functions in SolidStart / Guides / Caching