set up demo mode

backend/knexfile.js

@@ -20,6 +20,25 @@ module.exports = {
     },
   },
 
+  demo: {
+    client: "postgresql",
+    connection: {
+      host: "db",
+      port: process.env.DB_PORT,
+      database: process.env.DB_NAME,
+      user: process.env.DB_USER,
+      password: process.env.DB_PASSWORD,
+    },
+    pool: {
+      min: 2,
+      max: 10,
+    },
+    migrations: {
+      tableName: "knex_migrations",
+      directory: "./migrations",
+    },
+  },
+
   production: {
     client: "postgresql",
     connection: {