Pallet proc macro doc improvements (#7955)

* Fix weight syntax in comments

* Mention to add `IsType` bound

* Link to subsee

* Fix link

* Update frame/support/procedural/src/pallet/parse/call.rs

Co-authored-by: David <dvdplm@gmail.com>

* Apply review suggestion from @dvdplm, make StorageInstance doc link

* fix ui test

Co-authored-by: David <dvdplm@gmail.com>
Co-authored-by: thiolliere <gui.thiolliere@gmail.com>

substrate/frame/support/test/tests/pallet_ui/call_missing_weight.stderr

@@ -1,4 +1,4 @@
-error: Invalid pallet::call, require weight attribute i.e. `#[pallet::weight = $expr]`
+error: Invalid pallet::call, requires weight attribute i.e. `#[pallet::weight($expr)]`
   --> $DIR/call_missing_weight.rs:17:3
    |
 17 |         fn foo(origin: OriginFor<T>) -> DispatchResultWithPostInfo {}