Make Staking pallet using a proper Time module. (#4662)

* add new trait, still migration to make

* Apply suggestions from code review

Co-Authored-By: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

* implement migration

* better naming

* fix test

* no longer require DeprecatedTime

* add test

* fix version

* upgrade only from kusama

* add test

* fix test

* Update frame/timestamp/src/lib.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>
Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

substrate/primitives/timestamp/src/lib.rs

@@ -77,6 +77,7 @@ impl TimestampInherentData for InherentData {
 	}
 }
 
+/// Provide duration since unix epoch in millisecond for timestamp inherent.
 #[cfg(feature = "std")]
 pub struct InherentDataProvider;