ci: add production docker-compose for Portainer stack

Uses registry image instead of build context.
CI will push to gitlab.impresion3d.pro/root/davidaragon-portfolio:latest

docker-compose.prod.yml

@@ -0,0 +1,17 @@
+version: "3.8"
+
+services:
+  portfolio:
+    image: gitlab.impresion3d.pro/root/davidaragon-portfolio:latest
+    container_name: davidaragon-portfolio
+    ports:
+      - "8081:80"
+    restart: unless-stopped
+    environment:
+      - NODE_ENV=production
+    healthcheck:
+      test: ["CMD", "wget", "--no-verbose", "--tries=1", "--spider", "http://localhost/"]
+      interval: 30s
+      timeout: 3s
+      retries: 3
+      start_period: 5s