Support rel=modulepreload for automatic Link header generation

Hello!

Automatic Link header generation (https://developers.cloudflare.com/pages/platform/early-hints/#2-automatic-link-header-generation) is super useful, however it is currently only supported for <link> elements with rel=preconnect or rel=preload.

Since rel=modulepreload is the suggested method to preload module files, it would be great if these can be included in automatic header generation, too.

PS: I also don’t quite understand the restriction to exclude preload directives with the crossorigin attribute set, so if that restriction can be lifted that would be great for us, too.