Refresh Github token for non-migrated users who are invited to an organization

[drewbo]

Current federalist users who are invited to an organization but haven't migrated will have a GH token that won't have allowed third-party access from the Pages Production access. We need to remove their current token so they can re-authorize with Github using the provided button. h/t @Ephraim-G for identifying this potential issue earlier today

Acceptance Criteria

• [ ] When a current Federalist user who has NOT migrated their account to pages.cloud.gov is invited to a Pages organization, we delete the invited user's Github token so they will have to reauthorize their account with a new Pages Github Token.
• [ ] Allow a user to refresh their Github token from the same component that allows them to connect their Github account to Pages.