The playbook can install and configure docker-postgres-backup-local for you via the ansible-role-postgres-backup Ansible role.
For details about configuring and installing it, you can check them via:
roles/galaxy/postgres_backup/docs/configuring-postgres-backup.md locally, if you have fetched the Ansible rolesNote: for a more complete backup solution (one that includes not only Postgres, but also other configuration/data files), you may wish to look into BorgBackup instead.