Add optional Postgres backup service

docker/pg_backup/backup.sh

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+: "${POSTGRES_HOST:?}"
+: "${POSTGRES_USER:?}"
+: "${POSTGRES_PASSWORD:?}"
+: "${POSTGRES_DB:?}"
+
+backup_retention_days="${BACKUP_RETENTION_DAYS:-7}"
+
+export PGPASSWORD="$POSTGRES_PASSWORD"
+
+backup_dir="/backups"
+timestamp="$(date +%Y%m%d_%H%M%S)"
+backup_path="${backup_dir}/${POSTGRES_DB}_${timestamp}.dump"
+
+mkdir -p "$backup_dir"
+
+pg_dump -h "$POSTGRES_HOST" -U "$POSTGRES_USER" -d "$POSTGRES_DB" -F c -f "$backup_path"
+
+find "$backup_dir" -type f -name "*.dump" -mtime "+${backup_retention_days}" -delete