Add environment variables for Postiz service in docker-compose.yml

- Introduced DATABASE_URL, REDIS_URL, and JWT_SECRET environment variables to the Postiz service configuration.
- This enhancement improves the service's connectivity and security by ensuring necessary configurations are set for database and Redis access.

docker-compose.yml

@@ -609,6 +609,10 @@ services:
     volumes:
       - postiz-config:/config
       - postiz-uploads:/uploads
+    environment:
+      - DATABASE_URL=postgresql://postgres:${POSTGRES_PASSWORD}@postgres:5432/postgres?schema=postiz
+      - REDIS_URL=redis://redis:6379
+      - JWT_SECRET=${JWT_SECRET}
     depends_on:
       postgres:
         condition: service_healthy