update GitHub oAuth apps for Pages rollout

[amirbey]

User Story

A federalist-user should be able to login to the Pages app.

Background (Optional)

Update federalist-users oAuth app

Acceptance Criteria

Production app:

• [ ] update Application name from federalist.18f.gov to pages.cloud.gov
• [ ] update Homepage URL from https://federalistapp.18f.gov to https://app.pages.cloud.gov
• [ ] update Authorization callback URL from https://federalistapp.18f.gov to https://app.pages.cloud.gov

Staging app:

• [ ] update Application name from federalist-staging.18f.gov to pages-staging.cloud.gov
• [ ] update Homepage URL from https://federalistapp-staging.18f.gov to https://app.pages-staging.cloud.gov
• [ ] update Authorization callback URL from https://federalistapp-staging.18f.gov to https://app.pages-staging.cloud.gov

After evaluating, edit this part:

Level of effort - <low/medium/high>

Implementation outline (if higher than "low" effort):

• [ ] <TODO>