Allow tipping to only verified publishers

[NejcZdovc]

Resolves brave/brave-browser#2785

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:

plan 1

• enable rewards
• claim grant
• go to verified site and youtube channel
• make sure that you can tip that site

plan 2

• enable rewards
• claim grant
• go to non-verified site and youtube channel
• make sure that you can't tip that site

plan 3

• start browser from the master
• add some verified and non verified sites/channels to monthly tip
• switch to this PR branch
• make sure that only verified sites/channel are in the tables
• wait for contribution to happen and make sure that it went out just to verified publishers

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

[NejcZdovc]

closing as this is not desired behaviour anymore