Integrate playit.gg account creation

[seliayeu]

You can sign up for playit.gg through the CLI using APIs found in playit-agent.
The signup process works by repeatedly POSTing to an endpoint which send back a signup URL on the first request and sends updates regarding the signup process on subsequent requests. After the process finishes, you call another endpoint in order to obtain a secret key.

We need to implement a way to go through this process in the Lodestone client. The backend should probably handle the repeated pinging and update the frontend like is done in the playit-agent code.

It might be good to encourage the user to sign up if we plan on adding support for stuff like tunnel management since there doesn't appear to be a way to log back into your guest account if lose your session cookie.