Function page_front_matter_with_extra 

pub fn page_front_matter_with_extra(
    title: &str,
    weight: u32,
    extra_toml: &str,
    body: &str,
) -> String

Front matter for a docs page that also needs an [extra] table.

An example is a page that opts into Mermaid rendering with extra.mermaid = true. The extra_toml is the raw body of the [extra] table: one key = value per line, with no [extra] header around it.