pub fn include_file(mut self, path: impl AsRef<Path>) -> Self {
        self.include_file = Some(path.as_ref().to_path_buf());
        self
    }
Configures the optional module filename for easy inclusion of all generated Rust files

If set, generates a file (inside the `OUT_DIR` or `out_dir()` as appropriate) which contains
a set of `pub mod XXX` statements combining to load all Rust files generated.  This can allow
for a shortcut where multiple related proto files have been compiled together resulting in
a semi-complex set of includes.
tonic-build/src/prost.rs