Adds hard coded text for welcome panel

[NejcZdovc]

Resolves brave/brave-browser#1838

UI implementation: brave/brave-ui#248

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
  • Windows
  • macOS
  • Linux
• Verified that these changes pass automated tests (npm test brave_unit_tests && npm test brave_browser_tests) on
  • Windows
  • macOS
  • Linux
• 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

Test Plan:

• clean profile
• click on BAT logo
• click join button
• make sure that waiting button has en test

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

[bsclifton]

Original work done in brave/brave-ui#248 (approved and merged)

LGTM 😄 👍

[bsclifton]

master 991937f
0.57.x 12226c0
0.56.x 4b0d338