Add --toc-depth support in Typst template

[cderv]

Typst has support for a depth in TOC

https://typst.app/docs/reference/model/outline/#parameters-depth

Currently it is set to none in template

pandoc/data/templates/default.typst

Lines 76 to 81 in e7348b4

	$if(toc)$
	#outline(
	title: auto,
	depth: none
	);
	$endif$

I believe if the Typst writer does handle --toc-depth options like some other template, it could be possible to set $toc-depth$ variable in the template. This would allow to control like other formats.

Typst specific: Typst allows a value of none to have no depth limit, while default in Pandoc is toc-depth: 3.
If the default is used for Typst, there is the question of adding a way to pass toc-depth: none somehow, or another value that would mean no limit. toc-depth: 6 is the max value, and could be used for that maybe.

Context: We have added support for this in Quarto (https://github.com/quarto-dev/quarto-cli/pull/7825/files)