Github Action to deploy to AKS

[neilboyd]

Change kubernetes-secrets.yml to use the names from kubernetes.yml as values and replace them in the action, eg

runkeeper-client-id: "RUNKEEPER_CLIENT_ID"

Also for the web settings WEB_ROOT and ALLOWED_HOSTS. They're not really secrets, but do them the same way.

Then do what he describes here:
https://channel9.msdn.com/Events/dotnetConf/2020/Level-up-Your-DevOps-with-GitHub-Actions-and-Kubernetes
https://github.com/robrich/levelup-devops-github-actions-kubernetes

And also for the worker: replicas and TOTAL_SYNC_WORKERS - should both be the same value.
That's a bit trickier - created issue #30.