Diagnostics for label traits (#17441)

# Objective

Diagnostics for labels don't suggest how to best implement them.
```
error[E0277]: the trait bound `Label: ScheduleLabel` is not satisfied
   --> src/main.rs:15:35
    |
15  |     let mut sched = Schedule::new(Label);
    |                     ------------- ^^^^^ the trait `ScheduleLabel` is not implemented for `Label`
    |                     |
    |                     required by a bound introduced by this call
    |
    = help: the trait `ScheduleLabel` is implemented for `Interned<(dyn ScheduleLabel + 'static)>`
note: required by a bound in `bevy_ecs::schedule::Schedule::new`
   --> /home/vj/workspace/rust/bevy/crates/bevy_ecs/src/schedule/schedule.rs:297:28
    |
297 |     pub fn new(label: impl ScheduleLabel) -> Self {
    |                            ^^^^^^^^^^^^^ required by this bound in `Schedule::new`
```

## Solution

`diagnostics::on_unimplemented` and `diagnostics::do_not_recommend`

## Showcase

New error message:
```
error[E0277]: the trait bound `Label: ScheduleLabel` is not satisfied
   --> src/main.rs:15:35
    |
15  |     let mut sched = Schedule::new(Label);
    |                     ------------- ^^^^^ the trait `ScheduleLabel` is not implemented for `Label`
    |                     |
    |                     required by a bound introduced by this call
    |
    = note: consider annotating `Label` with `#[derive(ScheduleLabel)]`
note: required by a bound in `bevy_ecs::schedule::Schedule::new`
   --> /home/vj/workspace/rust/bevy/crates/bevy_ecs/src/schedule/schedule.rs:297:28
    |
297 |     pub fn new(label: impl ScheduleLabel) -> Self {
    |                            ^^^^^^^^^^^^^ required by this bound in `Schedule::new`
```

crates/bevy_app/src/app.rs

@@ -32,6 +32,9 @@ use std::{
 
 bevy_ecs::define_label!(
     /// A strongly-typed class of labels used to identify an [`App`].
+    #[diagnostic::on_unimplemented(
+        note = "consider annotating `{Self}` with `#[derive(AppLabel)]`"
+    )]
     AppLabel,
     APP_LABEL_INTERNER
 );

crates/bevy_ecs/src/schedule/set.rs

@@ -20,12 +20,18 @@ use crate::{
 
 define_label!(
     /// A strongly-typed class of labels used to identify a [`Schedule`](crate::schedule::Schedule).
+    #[diagnostic::on_unimplemented(
+        note = "consider annotating `{Self}` with `#[derive(ScheduleLabel)]`"
+    )]
     ScheduleLabel,
     SCHEDULE_LABEL_INTERNER
 );
 
 define_label!(
     /// Types that identify logical groups of systems.
+    #[diagnostic::on_unimplemented(
+        note = "consider annotating `{Self}` with `#[derive(SystemSet)]`"
+    )]
     SystemSet,
     SYSTEM_SET_INTERNER,
     extra_methods: {

crates/bevy_render/src/render_graph/graph.rs

@@ -14,6 +14,9 @@ use super::{EdgeExistence, InternedRenderLabel, IntoRenderNodeArray};
 pub use bevy_render_macros::RenderSubGraph;
 
 define_label!(
+    #[diagnostic::on_unimplemented(
+        note = "consider annotating `{Self}` with `#[derive(RenderSubGraph)]`"
+    )]
     /// A strongly-typed class of labels used to identify a [`SubGraph`] in a render graph.
     RenderSubGraph,
     RENDER_SUB_GRAPH_INTERNER

crates/bevy_render/src/render_graph/node.rs

@@ -23,6 +23,9 @@ pub use bevy_render_macros::RenderLabel;
 use super::{InternedRenderSubGraph, RenderSubGraph};
 
 define_label!(
+    #[diagnostic::on_unimplemented(
+        note = "consider annotating `{Self}` with `#[derive(RenderLabel)]`"
+    )]
     /// A strongly-typed class of labels used to identify a [`Node`] in a render graph.
     RenderLabel,
     RENDER_LABEL_INTERNER