refactor(models): remove 'is_readonly' attribute from multiple database models for consistency

app/Models/StandalonePostgresql.php

@@ -29,7 +29,6 @@ class StandalonePostgresql extends BaseModel
                 'host_path' => null,
                 'resource_id' => $database->id,
                 'resource_type' => $database->getMorphClass(),
-                'is_readonly' => true,
             ]);
         });
         static::forceDeleting(function ($database) {