Minor improvements

[chbatey]

While creating a deployment guide for Akka Cluster in Kubernetes keeping track of some changes we should make to this sample.

• Remove the NAMESPACE env var,
• Remove the service name and let the name of the actor system be used
• Remove Akka remoting port
• Remove readiness/liveness probes period overrides
• either use the app label or the akkaSystem label, don't have both

[chbatey]

• Change image name not to use scala/java so the same image name can be used in the deployment guide