[12x.] Add 0 option for disabling LongWaitDetected notification in Horizon docs (#10796)

* Add 0 option for disabling LongWaitDetectedNotification in horizon docs

* Update horizon.md

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Co-authored-by: Taylor Otwell <taylor@laravel.com>

Author: amirhshokri

horizon.md

@@ -653,6 +653,8 @@ You may configure how many seconds are considered a "long wait" within your appl
 ],
 ```
 
+Setting a queue's threshold to `0` will disable long wait notifications for that queue.
+
 <a name="metrics"></a>
 ## Metrics