Add android onboarding study

[deeppandya]

Resolves : #1281

[github-actions]

✅ Test Seed Generated Successfully

To apply the test seed:

1. Desktop: Launch the browser with --variations-pr=1282.
   Android: Set the command line to --variations-pr=1282 in debug menu, restart the browser.
   iOS: Set Variations PR to 1282 in Brave Core Switches debug menu, restart the browser.
2. Wait 5-10 seconds to fetch the seed.
3. Restart the browser to apply the seed.
4. Ensure Active Variations section at brave://version starts with the expected seed version (see below).

Seed Details

Parameter	Value
Version	pull/1282@2912c808f093ec8f393a955d414b3299006a6c50
Uploaded	Tue, 17 Dec 2024 16:47:52 GMT
PR commit	4a99a1d
Base commit	7970395
Merge commit	2912c80
Serial number	d32b35cf61c733c594663074b0fd0edc

[kjozwiak]

Blocked till brave/brave-core#26999 is merged into master and uplifted/released via 1.73.x. Once the new flag is pushed and 1.73.x is set at 100%, we'll push the above. We're also changing the above via:

• Nightly & BETA will be set at 100% form the start
• Release will start at 25% as discussed on Slack

CCing @timchilds

[kjozwiak]

Uplift into main/production approved after deliberating with @brave/uplift-approvers.

[kjozwiak]

Verification PASSED on Pixel 6 running Android 15 using the following build(s):

Nightly - AndroidOnboardingStudy:Enabled

Brave | 1.75.118 Chromium: 132.0.6834.57 (Official Build) canary (64-bit)
--- | ---
Revision | 7ad77ca4173af4e4eed04688bdb2f8752acd6800
OS | Android 15; Build/BP11.241121.010; 35; REL

• installed/launched 1.75.118 Chromium: 132.0.6834.57
• ensured that the new onboarding is being used re: the system modal appearing right after the Brave animation re: setting Brave as the default browser
• ensured that AndroidOnboardingStudy:Enabled via brave://version

screen-20241223-130551.mp4

BETA - AndroidOnboardingStudy:Enabled

Brave | 1.74.33 Chromium: 132.0.6834.57 (Official Build) beta (64-bit)
--- | ---
Revision | 7c275fd7e15fff5e960f2505bc49639361866c5b
OS | Android 15; Build/BP11.241121.010; 35; REL

• installed/launched 1.74.33 Chromium: 132.0.6834.57
• ensured that the new onboarding is being used re: the system modal appearing right after the Brave animation re: setting Brave as the default browser
• ensured that AndroidOnboardingStudy:Enabled via brave://version

screen-20241223-131649.mp4

Release - AndroidOnboardingStudy:Default

Brave | 1.73.104 Chromium: 131.0.6778.204 (Official Build) (64-bit)
--- | ---
Revision | 215b794a7c1f3e28151d0f7712e32c71be48775c
OS | Android 15; Build/BP11.241121.010; 35; REL

• installed/launched 1.73.104 Chromium: 131.0.6778.204 via GPS
• ensured that the previous onboarding is being used:
  • system notification permission modal
  • onboarding modeal which requires selecting "Make Default" before receiving the system default modal
  • P3A modal
• ensured that AndroidOnboardingStudy:Default via brave://version

screen-20241223-133252.mp4

Release - AndroidOnboardingStudy:Enabled

Brave | 1.73.104 Chromium: 131.0.6778.204 (Official Build) (64-bit)
--- | ---
Revision | 215b794a7c1f3e28151d0f7712e32c71be48775c
OS | Android 15; Build/BP11.241121.010; 35; REL

• installed/launched 1.73.104 Chromium: 131.0.6778.204 via GPS
• ensured that the new onboarding is being used re: the system modal appearing right after the Brave animation re: setting Brave as the default browser
• ensured that AndroidOnboardingStudy:Enabled via brave://version

screen-20241223-134452.mp4