fix: add event handler to delete the site when the related app deleted (#5282)

api/events/event_handlers/__init__.py

 from .create_site_record_when_app_created import handle
 from .deduct_quota_when_messaeg_created import handle
 from .delete_installed_app_when_app_deleted import handle
+from .delete_site_record_when_app_deleted import handle
 from .delete_tool_parameters_cache_when_sync_draft_workflow import handle
 from .delete_workflow_as_tool_when_app_deleted import handle
 from .update_app_dataset_join_when_app_model_config_updated import handle

api/events/event_handlers/delete_site_record_when_app_deleted.py

+from events.app_event import app_was_deleted
+from extensions.ext_database import db
+from models.model import Site
+
+
+@app_was_deleted.connect
+def handle(sender, **kwargs):
+    app = sender
+    site = db.session.query(Site).filter(Site.app_id == app.id).first()
+    db.session.delete(site)
+    db.session.commit()