set up postgres replication

[alee]

Currently using automated backup scripts e.g.

• https://wiki.postgresql.org/wiki/Automated_Backup_on_Linux

Should replace handrolled autopgsqlbackup with hot-standby replication

• https://github.com/nebirhos/docker-postgres-replication
• https://hub.docker.com/r/danieldent/postgres-replication
• https://wiki.postgresql.org/wiki/Replication,_Clustering,_and_Connection_Pooling