Promote URLs to hyperlinks in Rustdocs

[shaneutt]

Currently if you build rustdocs for the gateway-api package you'll find that many of the URLs we generate from the upstream Gateway API CRDs get flagged as non-hyperlinks:

$ cargo rustdoc --features k8s-openapi/v1_31 -p gateway-api
warning: this URL is not a hyperlink
   --> gateway-api/src/apis/experimental/grpcroutes.rs:644:9
    |
644 |     /// https://datatracker.ietf.org/doc/html/rfc2616#section-4.2).
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use an automatic link instead: `<https://datatracker.ietf.org/doc/html/rfc2616#section-4.2>`
    |
    = note: bare URLs are not automatically turned into clickable links
    = note: `#[warn(rustdoc::bare_urls)]` on by default

It would be more ideal if we could promote these to automatic links during kopium generate builds as per the suggestion above.