Handling GITHUB_TOKEN now with changelog support

[jasonkuhrt]

What

• builds were failing when trying to publish changelog https://github.com/prisma-labs/dripip/runs/608745979
• this was because a github release update requires github auth
• this means the github token available in workflows needs to be exposed to dripip as GITHUB_TOKEN env var https://help.github.com/en/actions/configuring-and-managing-workflows/authenticating-with-the-github_token
• [ ] there should be a pre-flight check for this
• [ ] there should be a flag to disable changelog which when present removes this preflight requirement. This should present the user with a command they can run to get the changelog that would have been published, so they can run later if desired