Add backup notice

[emerick]

Resolves brave/brave-browser#10021

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-Protections
  • 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:

• Clean profile
• Enable Rewards
• Restore wallet with user funds
• Wait for OnFetch callback
• Click on gear to bring up backup/restore modal
• Verify that modal text matches spec
• Verify that clicking the "connect to Uphold" link initiates the Uphold connection process
• Verify that you can switch back and forth between Backup/Restore tabs

---

• Clean profile
• Enable Rewards
• Claim promotion
• Wait for OnFetch callback
• Click on gear to bring up backup/restore modal
• "Backup" tab should show text from the spec
• Verify that clicking the "connect to Uphold" link in the modal notice initiates the Uphold connection process

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.

[NejcZdovc]

@emerick can we please move text for new users into backup tab, so that we are not stacking dialogs and we are just switching content based on user balance

[emerick]

@NejcZdovc Updated with browser tests but there's one small outstanding issue, see my comment above.

[emerick]

CI had a browser test failure on linux, restarting there. Ignoring test-install failure on Mac.

[emerick]

All CI is green now except for previously-noted test-install failure on Mac.