Introduce oAuth sync for Studio

[six7]

We'd like to offer users a way to use their Tokens Studio projects by just using oAuth, instead of API key and urn.

To do that, we need to prepare Studio a bit.

• 1.1 In the Figma plugin, offer a Log in with Studio button.
• 1.2 Once clicked, that button navigates to Studio.
• 1.3 If the user is logged already, confirm and show a screen Authenticated 🎉 You can now close this screen
• 1.4 If the user was not logged in, redirect to the login form, let them login
• 1.5 Once the user has logged in, show the same as in 1.3

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In addition, we'd like to prepare the plugin for oAuth for other providers, such as GitHub. Part of this issue should be to figure out how we can get that working, so that a user can log in with GitHub and then choose from their git projects to sync, instead of going the personal access tokens route as we do today.