Use crate documentation url

In the case of various crates we have for glib based libraries bindings, the documentations generated with a simple cargo doc don't contain any documentations due to licensing issues. As we can't "overwrite" the source files during the doc stage, because the files are read only, we opted for deploying our docs using CI ourselves.

Sadly, now once we will have a release, people looking for say gtk4 in docs.rs will end up with pretty poor quality docs instead of the one specified in Cargo.toml's documentation url.

I wonder if there's a possibility to make the docs.rs url point to that in such case instead of re-building the docs as part of docs.rs, it could be even something to opt-in for somehow.

See https://docs.rs/gtk/0.9.2/gtk/ for example instead of https://gtk-rs.org/docs/gtk/

Start by examining how docs.rs processes the documentation URL declared in Cargo.toml and how it currently builds crate documentation. Define the opt-in or eligibility behavior needed, then verify that eligible crates link to their declared documentation URL instead of generated docs.