Add random button for color background

[sangwoo108]

subtask of #15252.

Overall design also can be found there.

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When user toggles on a 'random button' for solid colors or gradient colors, we should set random background every time users open up NTP.

[stephendonner]

Verified PASSED using

Brave	1.45.74 Chromium: 106.0.5249.55 (Official Build) beta (x86_64)
Revision	4d5f098fca6ab7f4b6b7c240be3d9593c2357709-refs/branch-heads/5249@{#531}
OS	macOS Version 11.7 (Build 20G817)

Followed the testplan in brave/brave-core#14828, and confirmed that when Refresh on every new tab is checked, each new tab is in a different color.

example	example

[MadhaviSeelam]

Verification PASSED

Brave | 1.45.80 Chromium: 106.0.5249.65 (Official Build) beta (64-bit)
-- | --
Revision | 3269dc3633cdd2ab94546fdbe54962e45b17a6e0-refs/branch-heads/5249@{#580}
OS | Windows 11 Version 21H2 (Build 22000.978)

Solid Colors

Case 1: Toggle ON Refresh on every new tab

1. installed 1.45.80
2. launched Brave
3. opened a new-tab page
4. clicked on Customize
5. clicked on Solid colors card
6. toggle ON Refresh on every new tab
7. open NTP

Confirmed when Refresh on every new tab toggle is on, background color is picked on every new tab

step 5-6	step 7

Case 2: Toggle OFF Refresh on every new tab

1. click customize on the last tab from Case 1
2. click on selected solid color card to return to Refresh on every new tab
3. click toggle OFF Refresh on every new tab
4. open NTPs

Confirmed same background color will be picked from the last color in Case 1

Ex1	Ex2

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Verification passed on

Brave	1.45.90 Chromium: 106.0.5249.103 (Official Build) beta (64-bit)
Revision	182570408a1f25ab2731ef5f283b918df9b9f956-refs/branch-heads/5249_91@{#6}
OS	Ubuntu 18.04 LTS

Solid Colors

Case 1: Toggle ON Refresh on every new tab

1. installed 1.45.x
2. launched Brave
3. opened a new-tab page
4. clicked on Customize
5. clicked on Solid colors card
6. toggle ON Refresh on every new tab
7. open NTP

Confirmed when Refresh on every new tab toggle is on, background color is picked on every new tab

Case 2: Toggle OFF Refresh on every new tab

1. click customize on the last tab from Case 1
2. click on selected solid color card to return to Refresh on every new tab
3. click toggle OFF Refresh on every new tab
4. open NTPs

Confirmed same background color will be picked from the last color in Case 1