[iOS][DefaultBrowser] Implement the default browser video promo

This CL:
- Adds the MVC for the video default browser promo
- Adds two temporary lottie animations (light and dark mode).
- Adds the strings needed for the promo
- Does not attach the video promo to the default browser promo manager yet.

UI: https://drive.google.com/file/d/1J5gcWLhhWpXKMiyu-7DRaq1HSt68icG9/view?usp=sharing

Change-Id: I914f88017614b9f22b2d7d327181d38f9b13b0a9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4514481


Commit-Queue: Cheick Cisse <cheickcisse@google.com>
Reviewed-by: Robbie Gibson <rkgibson@google.com>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1145442}