[Backport 12.4] [TASK] Switch to confvals for mod.web_layout (#478)

* [TASK] Switch to confvals for mod.web_layout

* use confvals
* correct indentation
* correct header levels
* Give headers to examples

No other text changes made

releases: main, 12.4, 11.5

* Update Documentation/PageTsconfig/Mod/WebLayout.rst

Co-authored-by: Chris Müller <[email protected]>

* [TASK] Switch to confvals for mod.web_layout

* use confvals
* correct indentation
* correct header levels
* Give headers to examples

No other text changes made

releases: main, 12.4, 11.5

* Apply suggestions from code review

Co-authored-by: Chris Müller <[email protected]>

---------

Co-authored-by: lina.wolf <[email protected]>
Co-authored-by: Lina Wolf <[email protected]>
Co-authored-by: Chris Müller <[email protected]>
Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>