[unified-consent] Add learn-more URL to settings page

A learn-more question mark is added to the syncSetup page.

Bug: 863138
Cq-Include-Trybots: luci.chromium.try:closure_compilation
Change-Id: I3da65e76a7054c6c5256dc96f746c83968dc2e28
Reviewed-on: https://chromium-review.googlesource.com/1138247
Reviewed-by: Scott Chen <scottchen@chromium.org>
Commit-Queue: Thomas Tangl <tangltom@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575348}
2 files changed