Add Events to bevy_ecs prelude (#5159)

# Objective

This is a common and useful type. I frequently use this when working with `Events` resource directly, typically when caching the data or manipulating the `World` directly.

This is also useful when manually configuring the cleanup strategy for events.

crates/bevy_ecs/src/lib.rs

@@ -30,7 +30,7 @@ pub mod prelude {
         change_detection::DetectChanges,
         component::Component,
         entity::Entity,
-        event::{EventReader, EventWriter},
+        event::{EventReader, EventWriter, Events},
         query::{Added, AnyOf, ChangeTrackers, Changed, Or, QueryState, With, Without},
         schedule::{
             AmbiguitySetLabel, ExclusiveSystemDescriptorCoercion, ParallelSystemDescriptorCoercion,