Fix doc build with --all-features (#8277)

* implement

* make default pre/post_upgrade

* simplify Cargo.toml

* revert removal of outdated/private links

* link in pallet-mmr

substrate/bin/node-template/pallets/template/src/lib.rs

@@ -2,7 +2,7 @@
 
 /// Edit this file to define custom logic or remove it if it is not needed.
 /// Learn more about FRAME and the core library of Substrate FRAME pallets:
-/// https://substrate.dev/docs/en/knowledgebase/runtime/frame
+/// <https://substrate.dev/docs/en/knowledgebase/runtime/frame>
 
 pub use pallet::*;