Manning is based on SPG-Controls/patroni-etcd-docker.
Configs are set in the Dockerfile and the default patroni.yml. Environmental variables or some other configuration settings, including the etcd: block should likely be set according to your existing setup. The included configuration is included as a default. The environmental variables in the Dockerfile are generally required to run the container properly; again, these are merely defaults. Zalando has excellent documentation on both the YAML and environment configuration.
Environmental variables that need to be set on a per-container/service level include PATRONI_NAME, PATRONI_POSTGRESQL_CONNECT_ADDRESS and PATRONI_RESTAPI_CONNECT_ADDRESS.