Use next.config.mjs for CNA templates (#60494)

As `.mjs` support for `next.config` is stable now we can swap our
default to use it instead.

Closes NEXT-2052

packages/create-next-app/templates/app-tw/js/next.config.mjs

@@ -1,4 +1,4 @@
 /** @type {import('next').NextConfig} */
 const nextConfig = {}
 
-module.exports = nextConfig
+export default nextConfig

packages/create-next-app/templates/app-tw/ts/next.config.mjs

@@ -1,4 +1,4 @@
 /** @type {import('next').NextConfig} */
 const nextConfig = {}
 
-module.exports = nextConfig
+export default nextConfig

packages/create-next-app/templates/app/js/next.config.mjs

@@ -1,4 +1,4 @@
 /** @type {import('next').NextConfig} */
 const nextConfig = {}
 
-module.exports = nextConfig
+export default nextConfig

packages/create-next-app/templates/app/ts/next.config.mjs

@@ -1,4 +1,4 @@
 /** @type {import('next').NextConfig} */
 const nextConfig = {}
 
-module.exports = nextConfig
+export default nextConfig

packages/create-next-app/templates/default-tw/js/next.config.mjs

@@ -3,4 +3,4 @@ const nextConfig = {
   reactStrictMode: true,
 }
 
-module.exports = nextConfig
+export default nextConfig

packages/create-next-app/templates/default-tw/ts/next.config.mjs

@@ -3,4 +3,4 @@ const nextConfig = {
   reactStrictMode: true,
 }
 
-module.exports = nextConfig
+export default nextConfig

packages/create-next-app/templates/default/js/next.config.mjs

@@ -3,4 +3,4 @@ const nextConfig = {
   reactStrictMode: true,
 }
 
-module.exports = nextConfig
+export default nextConfig

packages/create-next-app/templates/default/ts/next.config.mjs

@@ -3,4 +3,4 @@ const nextConfig = {
   reactStrictMode: true,
 }
 
-module.exports = nextConfig
+export default nextConfig