Improve publish action to also push apps to Play Store

[garethbowen]

When switching to GH Actions I didn't quite get around to publishing the demo, gamma, and unbranded apps to the Play Store. This feature makes it easier to do QA because you can skip the manual step. All the code is there it just needs to be reactivated and tested. Make sure only these apps are published, and that they're published to the alpha channel.

Make sure the publish happens after the apk is uploaded to the GH Release so we don't regress on this issue.