https://github.com/mrts/docker-postgresql-multiple-databases
https://github.com/mrts/docker-postgresql-multiple-databases/blob/master/create-multiple-postgresql-databases.sh

https://dev.to/nietzscheson/multiples-postgres-databases-in-one-service-with-docker-compose-4fdf
### entrypoint.sh
#!/bin/bash

set -e
set -u

function create_user_and_database() {
    local database=$1
    echo "  Creating user and database '$database'"
    psql -v ON_ERROR_STOP=1 --username "$POSTGRES_USER" <<-EOSQL
        CREATE USER $database;
        CREATE DATABASE $database;
        GRANT ALL PRIVILEGES ON DATABASE $database TO $database;
  EOSQL
}

if [ -n "$POSTGRES_MULTIPLE_DATABASES" ]; then
    echo "Multiple database creation requested: $POSTGRES_MULTIPLE_DATABASES"
    for db in $(echo $POSTGRES_MULTIPLE_DATABASES | tr ',' ' '); do
        create_user_and_database $db
    done
    echo "Multiple databases created"
fi