Fix explicit Oauth flow

[heyitsaamir]

• Currently our oauth flow works well for SSO, but not for explicit Oauth.
• In explicit Oauth, the value for the tokenExchangeUrl is set to blank
  
• This means that this is NOT an SSO. When this is the case, the onTokenExchange will not be called. And this is the function which sets the storage value to indicate that an Oauth is actually happening. The onVerifyState checks if this value is present or not before proceeding.
• In this PR, we set this value when the oauth card is sent if the value of tokenExchangeUrl is not present.
• This also has the side effect of Oauth working normally in group chats.
• Question: Should we just get rid of this check in onVerifyState? It'll simplify the code, but I don't know what the implications of it are. @aacebo

Screen.Recording.2025-03-28.at.3.33.31.PM.mov

In this video, we're doing explicit Oauth in a group ^