feat: add Next.js CSR example

[raynerljm]

Problem

Our SDK currently lacks example apps demonstrating how to use our SDK. This introduces two problems

1. RPs do not have example apps following good practices to refer to
2. We are not able to easily test SDK changes with an app (we need to do an npm link)

Closes #384

Solution

Added an example Next.js app using CSR and API routes. It is hosted here.

Features:

• Primarily communicates with sgid-server via the src/pages/api routes
• Utilizes an in-memory store src/lib/store.js to store Session data (e.g. state, nonce, codeVerifier, etc.)

Tests

// TODO: ADD recording

[kwajiehao]

Left comments! happy to discuss them over a call as well

[raynerljm]

@kwajiehao also made the following changes based on comments from the Next.js SSR PR.

• Added the scopes and redirect URI to register in the README
• Let start:dev script do both the build and running

[kwajiehao]

lgtm