[CloudAP SSO] Re-add feature to attach some auth data as headers.

Currently, all auth data (proof of possession cookies) are appended to
the request's cookie header.

When the new feature is enabled, auth data whose name begins with
'x-ms-' will be added to the request as a separate header. All other
auth data will be appended to the request's cookie header.

The new code isn't covered by automated tests because this is a
temporary feature to probe where auth data should be attached in the
wild (i.e. outside of local builds). Eventually the feature (and one of
the auth data attachment methods) will be removed, and the remaining
implementation will be covered by tests.

This feature was previously added in https://crrev.com/c/4103847.

Bug: 1246839
Change-Id: If1d0ef333e748462337252abf835e0e251df9d36
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4433770
Reviewed-by: Owen Min <zmin@chromium.org>
Commit-Queue: Owen Min <zmin@chromium.org>
Code-Coverage: Findit <findit-for-me@appspot.gserviceaccount.com>
Auto-Submit: Igor Ruvinov <igorruvinov@chromium.org>
Commit-Queue: Igor Ruvinov <igorruvinov@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1131385}