Redirect html representation URLs

[distantnative]

Description

Summary of changes

• Requests for a page's html representation get redirected to the normal page URL without extension

Reasoning

Avoiding duplicate content, e.g. at https://getkirby.com/docs as well as https://getkirby.com/docs.html.

I have explained in #6509 (comment) why I think making Kirby stricter here and just delivering content if a docs.html.php template exists would be the wrong direction IMO, considering that within the Kirby system the one without any extension is directly tied to html as type. Having the option to have a docs.php alongside docs.html.php would be a contradiction.

Changelog

Fixes

• Requests for a page's html representation get redirected to the normal page URL without extension

Ready?

• In-code documentation (wherever needed)
• Unit tests for fixed bug/feature
• Tests and CI checks all pass

For review team

• Add changes & docs to release notes draft in Notion