set default cookie secret

medusa-config.js

@@ -72,7 +72,7 @@ const modules = {
 /** @type {import('@medusajs/medusa').ConfigModule["projectConfig"]} */
 const projectConfig = {
   jwt_secret: process.env.JWT_SECRET || "supersecret",
-  cookie_secret: process.env.COOKIE_SECRET,
+  cookie_secret: process.env.COOKIE_SECRET || "supersecret",
   store_cors: STORE_CORS,
   database_url: DATABASE_URL,
   admin_cors: ADMIN_CORS,