"Not linked in toc:" shouldn't fail on files included with `include` directive

[bmorelli25]

Summary

I have a file named output.md that is the output of a script. I do not want to include this file in the TOC. Instead, I include this file in a different markdown file using the include directive:

:::{include} scripts/codeowner-gen/output.md
:::

However, the build gives this fail because output.md is not included in the TOC:

:: fail: Documentation.Builder.Log[0] Not linked in toc: migration/scripts/codeowner-gen/output.md (/Users/brandon/Documents/GitHub/docs-builder/docs/source/docset.yml:)
:: info: DocumentationGenerator[0] Created documentation set for: /Users/brandon/Documents/GitHub/docs-builder/docs/source
:: info: DocumentationGenerator[0] Source directory: /Users/brandon/Documents/GitHub/docs-builder/docs/source Exists: True
:: info: DocumentationGenerator[0] Output directory: /Users/brandon/Documents/GitHub/docs-builder/.artifacts/docs/html Exists: True

[bmorelli25]

I wonder if it makes sense to add an orphan section to docset.yml where we can define these files without including them in the TOC. That would help us avoid losing track of files by still ensuring that all files are defined in some way in docset.yml

[Mpdreamz]

Two notes:

I think it would make senses to enforce includes come from _include folders. These would automatically be exempt from the TOC check. On top of that their usage will be immediately obvious. These _include folders may appear anywhere in the tree so they can be scoped logically.

Files can be excluded through globbing today e.g this PR that turns the root of docs-content into a docset but excludes README.md from participating in the docs build.

https://github.com/elastic/docs-content/blob/feature/move-to-docs-builder/docset.yml#L4

[Mpdreamz]

another benefit of enforcing includes to live in _include folders is that we can much easier assume the role of a markdown file programmatically and e.g warn of include files that are not actually included anywhere.

[bmorelli25]

Makes sense and ++ to implementing this