Update text for enabling Rewards from brave://settings/rewards

[emerick]

Resolves brave/brave-browser#19496

Submitter Checklist:

• I confirm that no security/privacy review is needed, or that I have requested one
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally: npm run test -- brave_browser_tests, npm run test -- brave_unit_tests, npm run lint, npm run gn_check, npm run tslint
• Ran git rebase master (if needed)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• New files have MPL-2.0 license header
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

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, 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-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

• Clean profile
• Visit brave://settings/rewards
• Verify that text item for enabling Rewards matches Missing hyperlinks for Brave rewards under Settings brave-browser#19496 (comment)

[emerick]

CI passed on all platforms except Linux; restarting for Linux.

[emerick]

Linux CI passed; ready for merge.

[kjozwiak]

Verification PASSED on Win 11 x64 using the following build:

Brave | 1.34.25 Chromium: 96.0.4664.45 (Official Build) nightly (64-bit)
-- | --
Revision | 76e4c1bb2ab4671b8beba3444e61c0f17584b2fc-refs/branch-heads/4664@{#947}
OS | Windows 11 Version 21H2 (Build 22000.318)

• ensured that the new text under brave://settings/rewards matches Missing hyperlinks for Brave rewards under Settings brave-browser#19496 (comment)
• ensured that clicking on the button always opens the rewards panel without any issues
• ensured that once rewards has been enabled, the button is removed and the rewards settings are visible

Text Change	Opening rewards panel	Rewards Enabled