Update prometheuscommunity/postgres-exporter to v0.17.1

[mfvanek]

See https://hub.docker.com/r/prometheuscommunity/postgres-exporter/tags

• https://github.com/mfvanek/useful-sql-scripts/blob/master/running_pg_in_docker/7.%20Monitoring%20with%20postgres_exporter/docker-compose.yml
• https://github.com/mfvanek/useful-sql-scripts/blob/master/running_pg_cluster_in_docker/1.%20Hello%20Postgres%20cluster/docker-compose.yml