Apply node maintenance mode to servers (#4421)

app/Models/Node.php

@@ -186,6 +186,11 @@ class Node extends Model
         );
     }
 
+    public function isUnderMaintenance(): bool
+    {
+        return $this->maintenance_mode;
+    }
+
     public function mounts(): HasManyThrough
     {
         return $this->hasManyThrough(Mount::class, MountNode::class, 'node_id', 'id', 'id', 'mount_id');

app/Models/Server.php

@@ -354,6 +354,7 @@ class Server extends Model
     {
         if (
             $this->isSuspended() ||
+            $this->node->isUnderMaintenance() ||
             !$this->isInstalled() ||
             $this->status === self::STATUS_RESTORING_BACKUP ||
             !is_null($this->transfer)