Add support for channels from the new Brave News API. These replace categoryName.

[fallaciousreasoning]

For now, this should be behind the BraveNewsV2 flag. It is a requirement to release the new UI.

[stephendonner]

@brave/qa-team hold off on testing this (and other feed/channel-related issues) until after the fixes for issues in https://bravesoftware.slack.com/archives/CU56GUJ1H/p1666975874847419 have been pushed to production.

And brave/brave-core#15749

[stephendonner]

Removing QA/Blocked; I believe everything needed for testing has landed in the client and/or pushed to prod 👍

[stephendonner]

Removing QA/Blocked; I believe everything needed for testing has landed in the client and/or pushed to prod 👍

Though it would be good to hold off until brave/brave-core#15808 is merged, I now realize (not technically blocked, but we'd have to re-do testing, since there are channel-related tweaks -- including the ability to be translatable -- in there).

[stephendonner]

Verification PASSED using

Brave	1.46.100 Chromium: 107.0.5304.91 (Official Build) dev (x86_64)
Revision	3d5948960d62418160796d5831a4d2d7d6c90fa8-refs/branch-heads/5304@{#1097}
OS	macOS Version 11.7.1 (Build 20G918)

Steps:

1. installed 1.46.100
2. launched Brave
3. clicked Skip welcome tour
4. scrolled down on the new-tab page
5. clicked on Show Brave News
6. confirmed the usual mix of news, sports, entertainment, health, etc. categories/feeds
7. loaded brave://flags
8. enabled the brave://flags/#brave-news-v2 flag
9. closed Brave
10. relaunched Brave
11. with the default Top Sources category followed, scrolled Brave News
12. confirmed Gamespot articles
13. unfollowed Top Sources
14. followed Entertainment, reloaded
15. scrolled Brave News
16. confirmed Gamespot articles, reloaded
17. unfollowed Entertainment
18. followed Gaming, reloaded
19. scrolled Brave News

Confirmed the Gamespot feed was present in the Entertainment, Gaming, and Top Sources categories, with articles, without directly following it.

Entertainment

Customize dialog	Gamespot in feed

Gaming

Customize dialog	Gamespot in feed

Top Sources

Customize dialog	Gamespot in feed