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>

assets/settings/default.json

@@ -76,7 +76,7 @@
   // or waits for a `copilot::Toggle`
   "show_copilot_suggestions": true,
   // Whether to show tabs and spaces in the editor.
-  // This setting can take two values:
+  // This setting can take three values:
   //
   // 1. Draw tabs and spaces only for the selected text (default):
   //    "selection"
@@ -183,7 +183,7 @@
     // Default height when the assistant is docked to the bottom.
     "default_height": 320,
     // The default OpenAI model to use when starting new conversations. This
-    // setting can take two values:
+    // setting can take three values:
     //
     // 1. "gpt-3.5-turbo-0613""
     // 2. "gpt-4-0613""
@@ -351,7 +351,7 @@
     //      }
     "working_directory": "current_project_directory",
     // Set the cursor blinking behavior in the terminal.
-    // May take 4 values:
+    // May take 3 values:
     //  1. Never blink the cursor, ignoring the terminal mode
     //         "blinking": "off",
     //  2. Default the cursor blink to off, but allow the terminal to