Add user choice handling callback

This CL modifies ManagedUserProfileNoticeHandler to take either
SigninChoiceCallback or SigninChoiceWithConfirmationCallback.
The new callback will allow for us to keep the dialog open until a
confirmation screen is shown to the user. This new callback
will be use for OIDC signins. Existing signins will not be affected.

Change-Id: Iba7b7df046a653cb18346aa299cc686677d282fa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5598508
Reviewed-by: David Roger <droger@chromium.org>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Commit-Queue: Yann Dago <ydago@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1313386}