refactor: migrate to rsc and app dir

app/api/newsletter2/route.ts

@@ -0,0 +1,14 @@
+import { NextResponse } from 'next/server'
+import { NewsletterAPI } from 'pliny/newsletter'
+import siteMetadata from '@/data/siteMetadata'
+
+export async function POST(request: Request) {
+  const res = await request.json()
+  console.log(res) // { email: 'test@example.com' }
+
+  return NextResponse.json({ res })
+  // return NewsletterAPI({
+  //   // @ts-ignore
+  //   provider: siteMetadata.newsletter.provider,
+  // })
+}