Adds new on boarding flow

[NejcZdovc]

Resolves brave/brave-browser#5518

UI PR: brave/brave-ui#522

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Verified that these changes build without errors on
  • Android
  • iOS
  • Linux
  • macOS
  • Windows
• Verified that these changes pass automated tests (unit, browser, security tests) on
  • iOS
  • Linux
  • macOS
  • Windows
• Verified that all lint errors/warnings are resolved (npm run lint)
• Ran git rebase master (if needed).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.
• Request a security/privacy review as needed.
• Add appropriate QA labels (QA/Yes or QA/No) to include the closed issue in milestone
• Public documentation has been updated as necessary. For instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protection-Mode
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Custom-Headers
  • https://github.com/brave/brave-browser/wiki/Web-compatibility-issues-with-tracking-protection
  • https://github.com/brave/brave-browser/wiki/QA-Guide

Test Plan:

• enable rewards
• open panel and click on verify wallet button
• make sure that new tab is opened with verify modal shown
• close that modal
• click on verify wallet button on rewards page
• make sure that modal is opened again
• click on verify
• make sure that uphold page is opened

Reviewer Checklist:

• New files have MPL-2.0 license header.
• Request a security/privacy review as needed.
• Adequate test coverage exists to prevent regressions
• Verify test plan is specified in PR before merging to source

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on.
• All relevant documentation has been updated.

[tmancey]

See comments as Copy is inconsistent

[tmancey]

Copy in other PR had a full-stop

[NejcZdovc]

Image in the issue don't have it brave/brave-browser#5518

[emerick]

LGTM

[emerick]

LGTM

same as image provided by design

[kjozwiak]

Went through the following test cases to ensure the PR was working before approving #3153:

• ensured that the new modal is being displayed whenever clicking on the following buttons/properties under brave://rewards/
  • Verify Wallet
  • Add Funds
  • Withdraw Funds
  • (verify) <-- next to the `Brave wallet is powered by Uphold
• ensured that pressing "X" closes the modal without any issues
• ensured that clicking on Verify Wallet opens uphold.com in the same tab
• ensured that once you press Verify Wallet within the modal, it doesn't get displayed for the second time
• Downloaded 0.70.42 CR: 76.0.3809.87, clicked on Verify Wallet on the old UI under brave://rewards/ and updated to 0.70.57 CR: 76.0.3809.100 and ensured the new modal isn't being displayed when clicking on the following:
  • Verify Wallet
  • Add Funds
  • Withdraw Funds
  • (verify) <-- next to the `Brave wallet is powered by Uphold