*: Use auto_doc_cfg instead of doc(cfg) attributes (#2983)

Co-authored-by: João Oliveira <hello@jxs.pt>
Co-authored-by: Thomas Eizinger <thomas@eizinger.io>

misc/prost-codec/src/lib.rs

@@ -1,3 +1,5 @@
+#![cfg_attr(docsrs, feature(doc_cfg, doc_auto_cfg))]
+
 use asynchronous_codec::{Decoder, Encoder};
 use bytes::BytesMut;
 use prost::Message;