chore(doc): Replace doc_auto_cfg config with doc_cfg (#2428)

## Motivation

`doc_auto_cfg` was merged into `doc_cfg` in
rust-lang/rust#138907.

## Solution

Replaces `doc_auto_cfg` config with `doc_cfg`. And uses `cargo-docs-rs`
to check with the same options used by docs.rs.

Author: tottoto

tonic-build/src/lib.rs

@@ -5,7 +5,7 @@
 )]
 #![doc(issue_tracker_base_url = "https://github.com/hyperium/tonic/issues/")]
 #![doc(test(no_crate_inject, attr(deny(rust_2018_idioms))))]
-#![cfg_attr(docsrs, feature(doc_auto_cfg))]
+#![cfg_attr(docsrs, feature(doc_cfg))]
 
 use proc_macro2::{Delimiter, Group, Ident, Literal, Punct, Spacing, Span, TokenStream};
 use quote::TokenStreamExt;

tonic-health/src/lib.rs

@@ -11,7 +11,7 @@
 )]
 #![doc(issue_tracker_base_url = "https://github.com/hyperium/tonic/issues/")]
 #![doc(test(no_crate_inject, attr(deny(rust_2018_idioms))))]
-#![cfg_attr(docsrs, feature(doc_auto_cfg))]
+#![cfg_attr(docsrs, feature(doc_cfg))]
 
 use std::fmt::{Display, Formatter};
 

tonic-reflection/src/lib.rs

@@ -5,7 +5,7 @@
 )]
 #![doc(issue_tracker_base_url = "https://github.com/hyperium/tonic/issues/")]
 #![doc(test(no_crate_inject, attr(deny(rust_2018_idioms))))]
-#![cfg_attr(docsrs, feature(doc_auto_cfg))]
+#![cfg_attr(docsrs, feature(doc_cfg))]
 
 mod generated {
     #![allow(unreachable_pub)]

tonic/src/lib.rs

@@ -97,7 +97,7 @@
 )]
 #![doc(issue_tracker_base_url = "https://github.com/hyperium/tonic/issues/")]
 #![doc(test(no_crate_inject, attr(deny(rust_2018_idioms))))]
-#![cfg_attr(docsrs, feature(doc_auto_cfg))]
+#![cfg_attr(docsrs, feature(doc_cfg))]
 
 pub mod body;
 pub mod client;