Add a way to end-to-end test OAuth2 flows

[porcellus]

• Integrate OAuth2Provider in the test app frontend and backend
  • Expose a test api to handle creating clients in e2e tests
• Integrate OAuth2Client into our test app backend
• Add a separate route in the test app frontend that has a single Login via SuperTokens (akin to what we have for TP login)
  • This should get the authorization url from OAuth2Client and redirect to it on button press
  • This should take the clientId from a queryparam
• Add a separate route in the test app frontend that handles the callbacks we get after starting a login process via the above route
  • This should call the signin API of the OAuth2Client
  • It should display session information after that happens or an error if it fails