Add Eche feature to multidevice page

- Adds new string search tags for Eche feature
- Adds new sections for new Eche feature

./out/Default/browser_tests --gtest_filter="OSSettingsMultideviceSubPageV3Test.*"
./out/Default/unit_tests
./out/Default/chromeos_unittests --gtest_filter="MultiDeviceSetupFeatureStateManagerImplTest.*"

Bug: 184137843
Test: Pass test cases.
Change-Id: I081ab2f81bce8b43df571228e3b39c1ade20a1c7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3124302


Reviewed-by: Jon Mann <jonmann@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Reviewed-by: Daniel Nishi <dhnishi@chromium.org>
Commit-Queue: Mavis Hsu <mavishsu@google.com>
Cr-Commit-Position: refs/heads/main@{#919125}