CI: markdown link checker (#7145)

* change (CI): markdown link checker

* Fix some invalid doc links (re-run of cargo-unleash gen-readme w/ fixes).

* Fix some invalid doc links

* Fix some invalid doc links

* Fix some links

* Fix some links

* Apply @bkchr suggestions from code review

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Fix more links

* Fix more links

* typo

* Fix more links

* Fix more links

* Ignore valid link .. check wrongly sees it as invalid

* Fix style issue

* Fix style issue

* change (CI): update style guide link

* change (lib): suggestions

Co-authored-by: Dan Forbes <dan@danforbes.dev>
Co-authored-by: Steve Degosserie <steve@parity.io>
Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

substrate/frame/example-offchain-worker/README.md

@@ -1,3 +1,4 @@
+<!-- markdown-link-check-disable -->
 # Offchain Worker Example Module
 
 The Offchain Worker Example: A simple pallet demonstrating
@@ -6,9 +7,9 @@ concepts, APIs and structures common to most offchain workers.
 Run `cargo doc --package pallet-example-offchain-worker --open` to view this module's
 documentation.
 
-- [`pallet_example_offchain_worker::Trait`](https://docs.rs/pallet-example-offchain-worker/latest/pallet_example_offchain_worker/trait.Trait.html)
-- [`Call`](https://docs.rs/pallet-example-offchain-worker/latest/pallet_example_offchain_worker/enum.Call.html)
-- [`Module`](https://docs.rs/pallet-example-offchain-worker/latest/pallet_example_offchain_worker/struct.Module.html)
+- [`pallet_example_offchain_worker::Trait`](./trait.Trait.html)
+- [`Call`](./enum.Call.html)
+- [`Module`](./struct.Module.html)
 
 
 ## Overview

substrate/frame/example-offchain-worker/src/lib.rs

@@ -15,6 +15,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//! <!-- markdown-link-check-disable -->
 //! # Offchain Worker Example Module
 //!
 //! The Offchain Worker Example: A simple pallet demonstrating