GitHub Actions for Firebase

This Action for firebase-tools enables arbitrary actions with the firebase command-line client. Starting with version v2.1.2 each version release will point to a versioned docker image allowing for hardening our pipeline (so things don't break when I do something dump). On top of this, you can also point to a master version if you would like to test out what might not be deployed into a release yet. If you want to add a message to a deployment (e.g. the Git commit message) you need to take extra care and escape the quotes or the YAML breaks. A normal service account key(json format) or a base64 encoded service account key with the needed permissions for what you are trying to deploy/update. If you're deploying functions, you would also need the Cloud Functions Developer role, and the Cloud Scheduler Admin for scheduled functions.