Improve conditions processing

[aobort]

• If conditions list is empty, fill it with all possible conditions in "False" state. This will allow to observe which phases cluster object should pass and already passed before it's in ready state (https://github.com/aenix-io/etcd-operator/blob/main/internal/controller/etcdcluster_controller.go#L75-L84).
• Move initiail conditions' list filling and further condition(s) state update to separate function. This will decrease complexity of Reconcile method, improve code readability and make it easier to add new conditions. (https://github.com/aenix-io/etcd-operator/blob/main/internal/controller/etcdcluster_controller.go#L102-L125)
• Update condition's lastTransitionTime only if the status changed