Adding Copy, Clone, Debug to derived traits of ExecutorKind (#9385)

While being nobody other's issue as far I can tell, I want to create a
trait I plan to implement on `App` where more than one schedule is
modified.
My workaround so far was working with a closure that returns an
`ExecutorKind` from a match of the method variable.

It makes it easier for me to being able to clone `ExecutorKind` and I
don't see this being controversial for others working with Bevy.

I did nothing more than adding `Clone` to the derived traits, no
migration guide needed.

(If this worked out then the GitHub editor is not too shabby.)

crates/bevy_ecs/src/schedule/executor/mod.rs

@@ -27,7 +27,7 @@ pub(super) trait SystemExecutor: Send + Sync {
 /// The default depends on the target platform:
 ///  - [`SingleThreaded`](ExecutorKind::SingleThreaded) on WASM.
 ///  - [`MultiThreaded`](ExecutorKind::MultiThreaded) everywhere else.
-#[derive(PartialEq, Eq, Default)]
+#[derive(PartialEq, Eq, Default, Debug, Copy, Clone)]
 pub enum ExecutorKind {
     /// Runs the schedule using a single thread.
     ///