feature: No-TOC YAML option

[pawamoy]

Is your feature request related to a problem? Please describe.

Sometimes we want to render an object's docs but not include its headings into the ToC, because we render it for documentation purposes (examples), and we don't need the entries in the ToC.

Describe the solution you'd like

An option to prevent adding any generated heading to the ToC.

Describe alternatives you've considered

In mkdocstrings-python's docs, we do this:

```md exec="on"
::: package.get_version
    options:
      heading_level: 3
      parameter_headings: true
      docstring_section_style: list
```

This effectively converts the Markdown in a sub-layer, preventing propagation of headings.

Additional context

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