docs: Add documentation for auto_update_extensions (#46130)

Add documentation for the existing `auto_update_extensions` setting that
allows users to toggle auto-updates per extension.

Release Notes:
- N/A

---------

Co-authored-by: Kunall Banerjee <hey@kimchiii.space>

docs/src/configuring-zed.md

@@ -244,6 +244,26 @@ Define extensions which should be installed (`true`) or never installed (`false`
 }
 ```
 
+## Auto Update extensions
+
+- Description: Define extensions to be autoupdated or manually updated.
+- Setting: `auto_update_extensions`
+- Default: `null`
+
+**Options**
+
+Define extensions which will be autoupdated (`true`) vs. those that will be manually updated (`false`).
+
+```json [settings]
+{
+  "auto_update_extensions": {
+    "html": true,
+    "dockerfile": true,
+    "docker-compose": false
+  }
+}
+```
+
 ## Autosave
 
 - Description: When to automatically save edited buffers.