examples: add example on Astro + Payload Local API (#10174)

Adds example on using the Local API (both fetching data and modifying
data) with Astro (vanilla JS)


https://github.com/user-attachments/assets/bf2dee99-2ad7-43f5-b809-1cf626051720

This is achieved through the monorepo:
```
website/
payload/
```

examples/astro/website/.env.example

@@ -0,0 +1,2 @@
+DATABASE_URI=mongodb://127.0.0.1/payload-template-blank-3-0
+PAYLOAD_SECRET=YOUR_SECRET_HERE