[Auth] Expand react-dapp-auth demo to allow for using an existing pairing topic flow to connect

[bkrem]

Context

• There are currently two ways to issue an auth_request to a wallet that also implements the Auth SDK:
  • New: on authClient.request(), a new pairing is created. This is communicated to the wallet out-of-band by scanning the generated QR code or pasting the generated URI into the wallet. Once the pairing is established the wallet can see the pending auth_request on the pairing topic and respond accordingly.
  • Known: if the described pairing steps have already been performed, the dapp can also pass the known pairing topic as an option for authClient.request()

Suggested changes

• The current Auth demo only covers the New flow described above.
• We need to create an affordance for a user to select an existing pairing (similarly to how https://react-app.walletconnect.com/ shows a modal to select from known pairings) to cover the Known flow.
• Tweaks and quick wins around responsiveness of the auth dapp demo would also be a useful improvement.

Additional context

• The demo counterpart for e2e testing is the react-wallet-auth deployment.