Support for custom annotations for EtcdCluster pods

[jsloyer]

https://github.com/coreos/etcd-operator/blob/b2a63ce924602be64a156361f3ee85498843026a/pkg/util/k8sutil/k8sutil.go#L83-L85 it looks like the annotations that get applied to EtcdCluster pods can not be changed. I was hoping to see if the operator supports custom annotations for the EtcdCluster pods. My use is being able to turn off mTLS for the EtcdCluster pods in a namespace.

If this is not supported any ideas on other ways to add annotations to the EtcdCluster pods or are you open to take a PR to add custom annotations to the EtcdCluster pods?