Use v2 promotion endpoints

[NejcZdovc]

Resolves #14980

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).
• 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. (Ask a Brave employee to help if you cannot access this document.)

Test Plan:

• run browser with the staging flag
• enable payments
• claim grant
• make sure that color that is selected matches the options
• dnd triangle to the wrong color and make sure that you get a new captcha
• dnd triangle to the correct color and make sure that grant is claimed successfully

Reviewer Checklist:

• Request a security/privacy review as needed if one was not already requested.

Tests

• Adequate test coverage exists to prevent regressions
• Tests should be independent and work correctly when run individually or as a suite ref
• New files have MPL2 license header

[NejcZdovc]

blocked on brave-intl/bat-client#93

[bsclifton]

Works great 👍

[bsclifton]

master 972e9b4
0.24.x 0a0ee2f
0.23.x b511d2e