Allow deploying stateless services as Deployments instead of StatefulSets

[HT154]

I know the operator used to use Deployments and they were phased out with v1beta2, but the reality is that StatefulSets don't make sense for most stateless services. The primary benefit of Deployments is the ability to perform rolling updates, which is completely orthogonal to how StatefulSets are implemented.

The operator should provide a way to select whether to use a StatefulSet or Deployment.

[jtimberman]

This would be a welcome feature. Most of the applications we're running internally in Kubernetes are stateless, or connect to database services that are external like AWS's RDS or Elasticache.