Support a release phase Procfile type in Hephy

[Cryptophobia]

Release phase enables you to run certain tasks before a new release of your app is deployed. Release phase can be useful for tasks such as:

Sending CSS, JS, and other assets from your app’s slug to a CDN or S3 bucket
Priming or invalidating cache stores
Running database schema migrations

The release command runs in a one-off dyno whenever a new release is created, unless the release is caused by changes to an add-on

https://devcenter.heroku.com/articles/release-phase

We should always urge developers to use zero-downtime migrations for release phase: https://blog.codeship.com/rails-migrations-zero-downtime/

This will require changes in the following components:

deis-builder
deis-controller
workflow-cli