Split postgres support into separate compose so that it defaults to sqlite instead

.env.sample

@@ -6,8 +6,6 @@ DOMAIN=n8n.example.com
 #EXTRA_DOMAINS=', `www.n8n.example.com`'
 LETS_ENCRYPT_ENV=production
 
-SECRET_DB_PASSWORD_VERSION=v1
-
 # Change to `true` to enable sending "anonymous" telemetry data to n8n
 # https://docs.n8n.io/reference/data-collection/
 N8N_DIAGNOSTICS_ENABLED=false
@@ -31,3 +29,7 @@ COMPOSE_FILE="compose.yml"
 #N8N_BASIC_AUTH_ACTIVE=true
 #N8N_BASIC_AUTH_USER=username
 #SECRET_ADMIN_PASSWORD_VERSION=v1
+
+# Use Postgres instead of SQLite
+#COMPOSE_FILE="$COMPOSE_FILE:compose.postgres.yml"
+#SECRET_DB_PASSWORD_VERSION=v1