Settable <header> and <footer> with bundled HTML export

Description

Would it be possible to use Typst' native syntax to specify a custom header and footer to be applied to every HTML page exported with the bundled feature?

Use Case

Imagine wanting to apply a static header and footer to each HTML page exported with the bundle export feature. One way of doing this using Typst' current feature set is by wrapping #document within a custom #my-document function:

#let my-document(title, body, ..options) = {
    document(title, ..options)[
        #html.header[
            This is an header.
        ]
        #body
        #html.footer[
            This is a footer.
        ]
    ]
}

However, if every HTML page to be served by the project resides in its own file, this requires importing #my-document every time at the top of the file using it.

How about using page.header and page.footer instead?

#set page(
    header: [This is an header],
    footer: [This is a footer.],
)

In this way, this set rule could be applied within a custom template, and subfiles or other HTML pages in general would not need to worry about using #my-document instead of #document.

Start by examining the bundled HTML export and the existing #html.header and #html.footer constructs described in the issue, then compare them with the proposed page.header and page.footer set rule. Done means a custom template can define a static header and footer once, and every bundled HTML page receives them without importing a wrapper document function.