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/client/consensus/babe/src/lib.rs

@@ -59,7 +59,7 @@
 //! blocks) and will go with the longest one in case of a tie.
 //!
 //! An in-depth description and analysis of the protocol can be found here:
-//! <https://research.web3.foundation/en/latest/polkadot/BABE/Babe.html>
+//! <https://research.web3.foundation/en/latest/polkadot/block-production/Babe.html>
 
 #![forbid(unsafe_code)]
 #![warn(missing_docs)]