editor: Show hints for using AI features on empty lines (#20824)

Co-Authored-by: Thorsten <thorsten@zed.dev>
Co-Authored-by: Antonio <antonio@zed.dev>

Screenshot:

![screenshot-2024-11-18-17 11
08@2x](https://github.com/user-attachments/assets/610fd7db-7476-4b9b-9465-a3d55df12340)

TODO:
- [x] docs

Release Notes:

- Added inline hints that guide users on how to invoke the inline
assistant and open the assistant panel. (These hints can be disabled by
setting `{"assistant": {"show_hints": false}}`.)

---------

Co-authored-by: Thorsten <thorsten@zed.dev>
Co-authored-by: Antonio <antonio@zed.dev>
Co-authored-by: Thorsten Ball <mrnugget@gmail.com>

docs/src/configuring-zed.md

@@ -2327,15 +2327,18 @@ Run the `theme selector: toggle` action in the command palette to see a current
 - Default:
 
 ```json
-"assistant": {
-  "enabled": true,
-  "button": true,
-  "dock": "right",
-  "default_width": 640,
-  "default_height": 320,
-  "provider": "openai",
-  "version": "1",
-},
+{
+  "assistant": {
+    "enabled": true,
+    "button": true,
+    "dock": "right",
+    "default_width": 640,
+    "default_height": 320,
+    "provider": "openai",
+    "version": "1",
+    "show_hints": true
+  }
+}
 ```
 
 ## Outline Panel