The frame time graph enabling is *weird*

## Bevy version and features

- 0.17.0-rc

## What you did

https://github.com/bevyengine/bevy/pull/19277 introduces a new frame graph to the FPS plugin. Cool! But I have my FPS overlay disabled on startup, so why am I seeing it? Oh, turns out that `FpsOverlayConfig.enabled` is ignored for this. You need to set the deeper nested `FpsOverlayConfig.frame_time_graph_config.enabled` to false.
That seems... unexpected?

Turns out I need to init it like this:
```rust
app.add_plugins(FpsOverlayPlugin {
config: FpsOverlayConfig {
enabled: false,
frame_time_graph_config: FrameTimeGraphConfig {
enabled: false,
..default()
},
..default()
},
});
```

And write my system like this:
```rust
fn toggle_fps_overlay(mut config: ResMut) {
config.enabled = !config.enabled;
config.frame_time_graph_config.enabled = config.enabled;
}
```