Support pre-provisioned external PostgreSQL for SpiceDB in Docker Compose

Problem A self-hosted operator using Formbricks 6.0.1 with externally managed PostgreSQL reports that the supplied Compose stack requires authzed-db-bootstrap and its POSTGRES_ADMIN_URL, even when the dedicated SpiceDB database and role have already been provisioned. Their application credentials intentionally cannot create roles/databases or alter ownership. Supplying provisioning credentials to the deployment broadens access to a shared PostgreSQL cluster. The operator currently patches the bootstrap script with exit 0 to retain the dependency chain; this is a workaround, not the desired implementation. Goal Provide a supported, documented Docker Compose deployment path for a pre-provisioned external PostgreSQL SpiceDB datastore using credentials scoped to that database, while retaining the existing bundled-PostgreSQL bootstrap path. Done when • An operator can configure the SpiceDB migration and runtime connection to an externally provisioned database, including its conn…