Enhanced llms.txt support

[davlgd]

This PR adds some features to llms.txt support, to better follow proposal spec:

• Link to markdown files
• Add an Optional section (use it with llmsTxtOptional: true in content front matter)

I only link 1st level sections, ordered alphabetically, but feel free to use different rules

[netlify]

✅ Deploy Preview for hugo-hextra ready!

Name	Link
🔨 Latest commit	c3381f8
🔍 Latest deploy log	https://app.netlify.com/projects/hugo-hextra/deploys/68c8f017f74ce700080b57b0
😎 Deploy Preview	https://deploy-preview-834--hugo-hextra.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify project configuration.

[imfing]

I believe it’s possible to disable llmstxt on a per-page basis using:
https://gohugo.io/configuration/outputs/#outputs-per-page

Would it also make sense to add documentation for the new Markdown output format?

[davlgd]

I believe it’s possible to disable llmstxt on a per-page basis using: https://gohugo.io/configuration/outputs/#outputs-per-page

I don't filter content but this implementation differs from current as it doesn't add "Root" pages and level 2 sections

Would it also make sense to add documentation for the new Markdown output format?

If this part of implementation is ok for you I can add it

PS : I've added it in a dedicated commit. For fa language, translation is incomplete

[imfing]

have a few questions. in addtion, given that we are adding param for "optional" content, would it make sense to also support exclude a page / section from llms.txt?

for example:

params:
  llmstxt:
    optional: true # default `false`
    exclude: true  # default `false`

[davlgd]

I've removed the title alphabetical sort and "Optional" section when there is no optional content

[davlgd]

have a few questions. in addtion, given that we are adding param for "optional" content, would it make sense to also support exclude a page / section from llms.txt?

for example:

params:
  llmstxt:
    optional: true # default `false`
    exclude: true  # default `false`

Yep, for example you maybe want to exclude blog from such listing to focus on core documentation (it's why there is an optional section at the beginning, to list useful but not mandatory documents).

I've also added an exclude parameter working on a per page/section basis (you can exclude a full section or only a single page).