Change Postgres config location

Previously, the postgres configuration file was added to the
/var/lib/postgresql/data directory which was overwritten by the
already-existing named data volume. When initializing a database,
the placement of the configuration file in /var/lib/postgresql/data
caused an error that the "PGDATA was not empty."

This commit fixes this issue by placing the configuration file in
a different location (/etc/postgresql) and then running the Dockerfile
entrypoint with an argument showing the location of the config file.

docker-compose.yml

@@ -39,6 +39,7 @@ services:
     volumes:
       - postgres_data:/var/lib/postgresql/data/
     restart: always
+    command: -c 'config_file=/etc/postgresql/postgresql.conf'
 
 volumes:
   postgres_data:

postgres/Dockerfile

@@ -1,4 +1,4 @@
 FROM postgres:14-alpine
-COPY postgresql.conf /var/lib/postgresql/data/postgresql.conf
+COPY postgresql.conf /etc/postgresql/postgresql.conf
 COPY postgres_backup.sh /usr/local/bin/postgres_backup.sh
 RUN chmod +x /usr/local/bin/postgres_backup.sh