docs: overlayBehavior

Author: hunterliu1003

docs/content/3.api/1.components/1.vue-final-modal.md

@@ -73,6 +73,15 @@ Hide the overlay or not.
     - JS: `Boolean`{lang=ts}
     - TS: `PropType<boolean>`{lang=ts}
   - Default: `undefined`{lang=ts}
+  - 
+### overlayBehavior
+
+Hide the overlay or not.
+  - Type:
+    - JS: `String`{lang=ts}
+    - TS: `PropType<'auto' | 'persist'>`{lang=ts}
+  - Default: `auto`{lang=ts}
+    - By default, the value of `overlayBehavior` will be `auto`. This means that when you open multiple modals, only the overlay of the top modal will be displayed. On the other hand, if you set the modal's `overlayBehavior` to `persist`, the modal's overlay will always be visible, allowing you to have multiple overlays at the same time.
 
 ### overlayTransition