Add missing "added in" to new environment variables in reference

[samypr100]

Summary

Adds the version for environment variables added in #16040 and #16125. as these were in-flight before documentation versioning was added.

Adds ability to emit a compiler error when added in is missing for improved reporting to the developer.

e.g. example for the ones fixed in this PR

error: missing #[attr_added_in("x.y.z")] on `UV_UPLOAD_HTTP_TIMEOUT`
       note: env vars for an upcoming release should be annotated with `#[attr_added_in("next release")]`
   --> crates\uv-static\src\env_vars.rs:593:15
    |
593 |     pub const UV_UPLOAD_HTTP_TIMEOUT: &'static str = "UV_UPLOAD_HTTP_TIMEOUT";
    |               ^^^^^^^^^^^^^^^^^^^^^^

error: missing #[attr_added_in("x.y.z")] on `UV_WORKING_DIRECTORY`
       note: env vars for an upcoming release should be annotated with `#[attr_added_in("next release")]`
    --> crates\uv-static\src\env_vars.rs:1087:15
     |
1087 |     pub const UV_WORKING_DIRECTORY: &'static str = "UV_WORKING_DIRECTORY";
     |               ^^^^^^^^^^^^^^^^^^^^
error: could not compile `uv-static` (lib) due to 2 previous errors