[10.x] Document maintenance mode with Horizon (#9233)

* Document maintenance mode with Horizon

* Update horizon.md

---------

Co-authored-by: Taylor Otwell <[email protected]>

horizon.md

@@ -86,6 +86,20 @@ As you can see in Horizon's default configuration file, each environment can con
 
 You may add additional supervisors to a given environment if you would like to define a new group of worker processes that should run in that environment. You may choose to do this if you would like to define a different balancing strategy or worker process count for a given queue used by your application.
 
+<a name="maintenance-mode"></a>
+#### Maintenance Mode
+
+While your application is in [maintainance mode](/docs/{{version}}/configuration#maintenance-mode), queued jobs will not be processed by Horizon unless the supervisor's `force` option is defined as `true` within the Horizon configuration file:
+
+    'environments' => [
+        'production' => [
+            'supervisor-1' => [
+                // ...
+                'force' => true,
+            ],
+        ],
+    ],
+
 <a name="default-values"></a>
 #### Default Values