example: add an example of using next.js

[markhughes]

This PR adds two next.js / react examples for using Voy both client-side and server-side 😄

For generating emddings:

• The client-side version uses the @visheratin/web-ai
• The server-side version uses @tensorflow-models/universal-sentence-encode with @tensorflow/tfjs-node

Start Page

Server Side Example

Client Side Example