[Feature Request] Add RemoveAccount API for long-running OBO

[pmaytak]

Is your feature request related to a problem? Please describe.
Currently there's no way to remove an account/token in a long running OBO scenario. A real-world example could be using a Graph delta API, where web API subscribes to receive some delta information periodically from Graph about a user. When a user calls the web API to unsubscribe, there should be a way to remove the OBO tokens for that user. Since long-running OBO tokens have a refresh token, there's no suggested cache expiry, so it's not set.

Describe the solution you'd like
Create an API something like RemoveAccountAsync(string longRunningOboKey) or StopLongRunningWebApi to not confuse it with normal OBO.