chore(example-apps): added nextjs example app (#2125)

Author: aryamohanan

example-apps/nextjs-app/.gitignore

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+.next

example-apps/nextjs-app/README.md

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+# Instana Next.js Example
+
+A simple Next.js app integrated with Instana.
+
+## Setup
+
+ESM loader is configured in `package.json`:
+
+```json
+"start": "NODE_OPTIONS='--import ./node_modules/@instana/collector/esm-register.mjs' INSTANA_DEBUG=true next start"
+```
+
+## Run the App
+
+```bash
+npm i
+npm run build
+npm run start
+```
+
+App runs at `http://localhost:3000`.
+
+## Routes
+
+* **Home:** `/` – Basic landing page
+* **API:** `/api/hello` – Returns `{ "message": "Hello from Instana-monitored Next.js API!" }`