feat(restarts): make resource restart limits opt-in

Default restart limits to zero for applications, previews, and services, and bump the Coolify version to 4.3.21.

app/Models/ApplicationPreview.php

@@ -13,6 +13,10 @@ class ApplicationPreview extends BaseModel
 {
     use HasRestartLimit, SoftDeletes;
 
+    protected $attributes = [
+        'max_restart_count' => 0,
+    ];
+
     protected $fillable = [
         'uuid',
         'application_id',