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/journal/src/journal.rs

@@ -15,9 +15,16 @@ use workspace::{AppState, OpenVisible, Workspace};
 
 actions!(journal, [NewJournalEntry]);
 
+/// Settings specific to journaling
 #[derive(Clone, Debug, Serialize, Deserialize, JsonSchema)]
 pub struct JournalSettings {
+    /// The path of the directory where journal entries are stored.
+    ///
+    /// Default: `~`
     pub path: Option<String>,
+    /// What format to display the hours in.
+    ///
+    /// Default: hour12
     pub hour_format: Option<HourFormat>,
 }