QuickStart: Add `FidoAssertionInfo`

Add a struct - `FidoAssertionInfo` - for passing information related to
the FIDO assertion to `SecondDeviceAuthBroker`.

Please check the attached bug for context and a design document.

Bug: b/259021973
Change-Id: I228fa91fdb5e9a1c5087f67d79c51d73f8237ba7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4055265


Reviewed-by: Jason Rhee <jasonrhee@google.com>
Commit-Queue: Kush Sinha <sinhak@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1076743}