Add tracing to `apply deferred`

I think that when debugging ordering-related issues it may be useful to see that apply deferred system was run, just like bevy traces other system executions.

This should be an easy task, but I'm creating an issue in case someone is against this change. I also want to mention that I'm new to tracing so I may miss something important here.

One spot where this even (or a scope maybe?) should be added is [here](https://github.com/bevyengine/bevy/blob/ec825d135b491e91079bbf907419e121aaaf7f36/crates/bevy_ecs/src/schedule/executor/multi_threaded.rs#L725), I believe.

But it is not the only one - there are other executors as well.