[N8N-4265] Improve docker compose setup with postgres (#3369)

* persist postgres data using docker volumes

* persist n8n data using docker volumes instead of writing to the host filesystem

* wait for postgres to be actually ready before starting the server

* run web server and workers as separate containers

* create a new `withPostgresAndWorker` example

docker/compose/withPostgresAndWorker/init-data.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+set -e;
+
+
+if [ -n "${POSTGRES_NON_ROOT_USER:-}" ] && [ -n "${POSTGRES_NON_ROOT_PASSWORD:-}" ]; then
+	psql -v ON_ERROR_STOP=1 --username "$POSTGRES_USER" --dbname "$POSTGRES_DB" <<-EOSQL
+		CREATE USER ${POSTGRES_NON_ROOT_USER} WITH PASSWORD '${POSTGRES_NON_ROOT_PASSWORD}';
+		GRANT ALL PRIVILEGES ON DATABASE ${POSTGRES_DB} TO ${POSTGRES_NON_ROOT_USER};
+	EOSQL
+else
+	echo "SETUP INFO: No Environment variables given!"
+fi