Add only headings of self to toctree

I think that https://github.com/sphinx-doc/sphinx/issues/2103 is related, but I am opening this as a separate issue because perhaps the functionality described there as missing is not the only way to achieve this end.

Consider a landing page in the documentation, say of how-to guides, that has a number of sub-pages (each one is a particular how-to guide).

A good landing page

For the page body, a sensitive author will use headings, descriptions and multiple toctrees to provide a structured overview of the sub-pages' content, by using multiple toctree directives, one for each section of the page:

How-to guides

Installation and configuration

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• Install in a VM
• Install with Docker
• Configure networking
• Configure flidgets
• Configure warbles

Production

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• Deploy
• Scale
• Replicate instances
• Upgrade in place
• Decommission

Observability and performance

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• Logging
• Monitoring
• Performance tuning

A poor menu

However, the navigation menu that's created does not benefit from this stucture, and by the time we get to more than about seven sub-pages, toctrees for that section of the navigation become rather unattractive and inconvenient to use - an undifferentiated list of items is a poor navigation interface.

A common pattern I see is a navigation menu that looks like:

• Home
• Tutorial
• How-to guides
  • Install in a VM
  • Install with Docker
  • Configure networking
  • Configure flidgets
  • Configure warbles
  • Deploy
  • Scale
  • Replicate instances
  • Upgrade in place
  • Decommission
  • Logging
  • Monitoring
  • Performance tuning
• Reference
• Explanation

This is well into the realm of being unwieldy, even with a certain amount of implict grouping. No user will enjoy working with that list.

A better menu

A much better pattern would be to add only the headings of the How-to landing page into the navigation menu:

• Home
• Tutorial
• How-to guides
  • Installation and configuration
  • Production
  • Observability and performance
• Reference
• Explanation

Achieving this requires two things:

• a toctree directive that add only the headings of self (strictly speaking, second-level headings and lower) into the toctree, but not display them in-situ in the page
• multiple toctree directives to list the particular sub-pages in each section, but not add them into the global navigation (an ordinary list of links could do this, but a toctree would be more elegant.

An alternative I've seen is to add another layer of nesting: a new landing page for each section of the how-to guides - but the result is an over-fussy and complex navigation structure.