Add / Exclude content for LLMS

[atinux]

I believe this is a great idea from @posva

• Allow content for llm only okineadev/vitepress-plugin-llms#42
• Exclude content from the generated llm-* files okineadev/vitepress-plugin-llms#43

[atinux]

I believe nuxt-llms can add for Nuxt Content those components:

• <llm-only>
• <llm-ignore>