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/call/src/call_settings.rs

@@ -11,6 +11,7 @@ pub struct CallSettings {
 
 #[derive(Clone, Default, Serialize, Deserialize, JsonSchema, Debug)]
 pub struct CallSettingsContent {
+    /// Whether the microphone should be muted when joining a channel or a call.
     pub mute_on_join: Option<bool>,
 }