Display setting documentation in settings.json (#3936)

Let this screenshot of settings.json speak for itself: 

![image](https://github.com/zed-industries/zed/assets/24362066/fca60383-1788-43f9-803b-00f083394c8a)

Release Notes:
- Added code completion & on-hover documentation to Zed's settings.json
file.

---------

Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>

crates/collab_ui/src/panel_settings.rs

@@ -28,8 +28,17 @@ pub struct NotificationPanelSettings {
 
 #[derive(Clone, Default, Serialize, Deserialize, JsonSchema, Debug)]
 pub struct PanelSettingsContent {
+    /// Whether to show the panel button in the status bar.
+    ///
+    /// Default: true
     pub button: Option<bool>,
+    /// Where to dock the panel.
+    ///
+    /// Default: left
     pub dock: Option<DockPosition>,
+    /// Default width of the panel in pixels.
+    ///
+    /// Default: 240
     pub default_width: Option<f32>,
 }