Include Maputnik style editor into the Martin binary

maputnik is an excellent style editor (now part of maplibre), but it is often complicated to combine maputnik with martin due to CORS. It is possible to combine them via docker compose and an nginx reverse proxy, but that's also combersome and complicated for novice users.

I think we should use actix_web_static_files or similar to build+package maputnik as part of the build.rs script, and include it inside the martin binary.