[CSC] Add signin flow test

1. If already signed in, skip the sign-in flow.
2. Also added an sync enum for the companion access point.

Bug: b/280536741
Change-Id: I6eccdceab94c839925e3bc85a882f8c3846c6b82
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4546596


Commit-Queue: Shakti Sahu <shaktisahu@chromium.org>
Reviewed-by: Michael Crouse <mcrouse@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1148182}