Propagate token-based enrollment config through enrollment flow

Add new modes and auth mechanism to EnrollmentConfig, along with the
enrollment_token field itself. These are set based on device state mode
prefs set during state determination (if a Flex token is found in the
OOBE configuration).

Add logic to propagate the token/mode through the
`EnrollmentScreen -> EnrollmentLauncher -> EnrollmentHandler ->
CloudPolicyClient -> DeviceManagementService` flow, eventually sending a
TokenBasedRegisterDeviceRequest (which basically just wraps a
DeviceRegisterRequest) to DMServer. Changes to CloudPolicyClient and
DeviceManagementService were added in the parent CL.

Bug: b/329271128
Test: browser_tests --gtest_filter=*EnrollmentScreen*
Test: unit_tests --gtest_filter=*EnrollmentConfig*
Change-Id: I97d7a39037a084f9312afbc7b7a1d05020ec3b09
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5389345


Reviewed-by: Sergiy Belozorov <sergiyb@chromium.org>
Commit-Queue: Jackson Tadie <jacksontadie@google.com>
Reviewed-by: Danila Kuzmin <dkuzmin@google.com>
Reviewed-by: Igor Ruvinov <igorruvinov@chromium.org>
Reviewed-by: Yves Arrouye <drcrash@chromium.org>
Reviewed-by: Artem Sumaneev <asumaneev@google.com>
Cr-Commit-Position: refs/heads/main@{#1289436}