Implement Updated GetTokenOrSignInResource pattern #43

New Token Service API to get the TokenResponse (if a token is available) or the SignInResponse in a single call. This reduces the initial sign in to a single request.

This was added by Core ABS team to improve pref of User Authorization Token acquire flows.

See :
microsoft/Agents-for-net#157 (initial)
microsoft/Agents-for-net#214 (refinement)