[EPIC] Enhancements on subdocs

[virgile-dev]

Feature Request

Is your feature request related to a problem or unsupported use case? Please describe. Subdocs need a little polish.

• Existing docs are hard to nest into another doc (UX and permissions)
• Pinned subdocs are not displayed on left pannel
• Subdocs and docs are not distinguished in the search modal
• Some subdocs are displayed in the doc index

Probably some other things Describe the solution you'd like A clear and concise description of what you want to happen. Add any considered drawbacks.

Describe alternatives you've considered A clear and concise description of any alternative solutions or features you've considered.

Discovery, Documentation, Adoption, Migration Strategy If you can, explain how users will be able to use this and possibly write out some documentation (if applicable). Maybe add a screenshot or design?

Do you want to work on it through a Pull Request?