chore(runtime-api-client/docs): add docs.rs metadata indicating that tracing module requires tracing feature

Author: jlizen

lambda-runtime-api-client/src/lib.rs

@@ -22,6 +22,7 @@ pub use error::*;
 pub mod body;
 
 #[cfg(feature = "tracing")]
+#[cfg_attr(docsrs, doc(cfg(feature = "tracing")))]
 pub mod tracing;
 
 /// API client to interact with the AWS Lambda Runtime API.