[Collaboration] Add authentication screens

Add signin and sync screens to the collaboration service.

Refactor FlowType enum into it's own file for use in Java.

https://screenshot.googleplex.com/BKzjAPav3rENfC7.png

Change-Id: I8e60cc44e88bd1e743391d87414cd0515b436153
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6142191
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Reviewed-by: Wenyu Fu <wenyufu@chromium.org>
Commit-Queue: Hailey Wang <haileywang@google.com>
Reviewed-by: Siddhartha S <ssid@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1407748}