clientv3/watch.go
func (e *Event) IsCreate() bool {
	return e.Type == EventTypePut && e.Kv.CreateRevision == e.Kv.ModRevision
}
func (e *Event) IsCreate() bool {
	return e.Type == EventTypePut && e.Kv.CreateRevision == e.Kv.ModRevision
}
// IsCreate returns true if the event tells that the key is newly created.