Authenticating in CI/CD

Add the following step to authorize the oban repo in GitHub Actions (or any other YAML based CI service):

- name: Authorize Oban
  run: |
    mix hex.repo add oban https://repo.oban.pro \
      --fetch-public-key SHA256:4/OSKi0NRF91QVVXlGAhb/BIMLnK8NHcx/EWs+aIWPc \
      --auth-key ${{secrets.oban_license_key}}

Be sure to add your oban_license_key to your GitHub organization's secrets storage.