Adds new event phase Initialization (#5302)

* Adds new event phase `Initialization`

Every event that was deposited inside of `on_initialize` was assigned to
the `ApplyExtrinsic(0)` phase which wasn't correct. This pr introduces a
new phase `Initialization`. This is the new phase while initializing
a block. After initialization we switch to `ApplyExtrinsic(N)` and at
the end to `Finalization` as before.

* Set `ExecutionPhase` in `initialize`

* Increment `spec_version`

substrate/frame/offences/src/tests.rs

@@ -129,7 +129,7 @@ fn should_deposit_event() {
 		assert_eq!(
 			System::events(),
 			vec![EventRecord {
-				phase: Phase::ApplyExtrinsic(0),
+				phase: Phase::Initialization,
 				event: TestEvent::offences(crate::Event::Offence(KIND, time_slot.encode())),
 				topics: vec![],
 			}]
@@ -164,7 +164,7 @@ fn doesnt_deposit_event_for_dups() {
 		assert_eq!(
 			System::events(),
 			vec![EventRecord {
-				phase: Phase::ApplyExtrinsic(0),
+				phase: Phase::Initialization,
 				event: TestEvent::offences(crate::Event::Offence(KIND, time_slot.encode())),
 				topics: vec![],
 			}]