fix(terraform/gcp): abandon SQL user on destroy (#29855)

google_sql_user.app issues DROP ROLE on destroy, which Postgres refuses
because the role owns every table the migrations job created (75
objects). The previous deletion_policy=ABANDON on google_sql_database
keeps the DB intact through destroy, so the role still owns its
objects. Set the same policy on the user; the instance deletion takes
both the database and the role with it anyway.

terraform/litellm/gcp/cloudsql.tf

@@ -108,6 +108,8 @@ resource "google_sql_user" "app" {
   name     = var.db_username
   instance = google_sql_database_instance.writer.name
   password = random_password.db_password.result
+
+  deletion_policy = "ABANDON"
 }
 
 resource "google_secret_manager_secret" "db_password" {