Add valueprop screen of Assistant consent flow

- The screen follows the current UX mock:
- The screen grab consent text through assistant setting manager.
- After user opt-in the screen send the consent request through
  assistant settings manager.
- Import necessary proto files for the consent flow.

Bug: b/78190629
Test: Manual Test
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I963e56cb1467906f9e17d7a0217da8a81b7a77a8
Commit-Queue: Yue Li <>
Reviewed-by: Xiyuan Xia <>
Reviewed-by: Xiaohui Chen <>
Cr-Commit-Position: refs/heads/master@{#559566}
22 files changed