Directly consume APK push configuration

[mitchhentges]

We have a single source of APK push configuration that currently lives in build-puppet. This push configuration is read by pushapkscript and tells it what channels exist for which tracks, which checks to use for which apps, the package name(s), and more.

This information is also valuable when using mozapkpublisher as a CLI, but can't be used at the moment. Instead, we have to pass in a ton of --skip-check flags and other information that could be static.

Instead, we should separate APK push configuration from pushapkscript configuration (credentials will still sit in pushapkscript config and be passed in as CLI args). Then, when doing a pushapk task, we should publish the current APK push configuration as an artifact.
Then, if we need to run the mozapkpublisher CLI directly, we can download the APK push configuration and point mozapkpublisher to it, allowing us to cut down the amount of CLI args that are needed.

TL;DR: cut down on mozapkpublisher CLI args by using the APK push config stored in build-puppet