Give users the ability to upload and use their own background images for the new tab page

This is sub task of https://github.com/brave/brave-browser/issues/15252

Overall design is described in https://github.com/brave/brave-browser/issues/15252.

• Specification
  • Custom image is per-profile configuration
  • Uploaded image is stored only in local device
  • After uploaded, NTP shows uploaded images by default
    • NTP SI will be displayed together if user doesn’t disable it
  • When user choose Brave backgrounds again after uploading custom image, stored image will be deleted

[btlechowski]

Verification passed on

Brave	1.37.83 Chromium: 99.0.4844.51 (Official Build) beta (64-bit)
Revision	d537ec02474b5afe23684e7963d538896c63ac77-refs/branch-heads/4844@{#875}
OS	Ubuntu 18.04 LTS

Verified test plan from https://github.com/brave/brave-core/pull/11622

Default image is brave background

Custom image

Verified able to chose custom background

Verified NTP SI was shown

Verified able to go back to brave background:

Dark theme

Logged: https://github.com/brave/brave-browser/issues/21518

[stephendonner]

Verified PASSED using

Brave	1.37.65 Chromium: 99.0.4844.35 (Official Build) nightly (64-bit)
Revision	f60a827ddb87f1c403e07713751a5551d5856ac0-refs/branch-heads/4844@{#579}
OS	Windows 10 Version 21H2 (Build 19044.1566)

Steps:

1. installed 1.37.65
2. launched Brave
3. opened a new-tab page
4. clicked on Customize on the lower right
5. chose Upload from device
6. confirmed the various images
7. restarted and confirmed they persisted after restart
8. chose Brave backgrounds
9. confirmed I could cycle through the various backgrounds
10. confirmed Sponsored Image ad backgrounds were still in the same position and frequency as before

clock.gif	clock.png	transparent-fire-gif.gif	lexus-is-350.jpg	Brave backgrounds (default)	Sponsored Image tabs

---

Verified PASSED using

Brave	1.37.91 Chromium: 99.0.4844.51 (Official Build) beta (x86_64)
Revision	d537ec02474b5afe23684e7963d538896c63ac77-refs/branch-heads/4844@{#875}
OS	macOS Version 12.3 (Build 21E230)

Steps:

1. installed 1.37.91
2. launched Brave
3. opened a new-tab page
4. clicked on Customize on the lower right
5. chose Upload from device
6. confirmed the various images
7. restarted and confirmed they persisted after restart
8. chose Brave backgrounds
9. confirmed I could cycle through the various backgrounds
10. confirmed Sponsored Image ad backgrounds were still in the same position and frequency as before

cute-transparent-gif-10.gif	Blue-Butterfly-PNG-Transparent-Image.png	lexus-is-350.jpg	Brave backgrounds (default)	Sponsored Image tabs