Limit controller object caches to only look at DevWorkspace-related resources

[amisevsk]

Description

The DevWorkspace Operator's controller caches a lot of Kubernetes objects (deployments, jobs, configmaps, secrets, serviceaccounts, pods, services, ingresses, routes). This means that the number of such objects on the cluster (even outside of those created for DevWorkspaces) impacts the memory usage of DWO in large clusters with many resources.

controller-runtime v0.9.0 has the beginnings of a system to restrict the controller cache to specific objects, in order to avoid the issue above.

Additional context

https://github.com/kubernetes-sigs/controller-runtime/blob/master/designs/use-selectors-at-cache.md