Add portName to event api portEvent

[etanshaul]

portEvents from the Event API currently look like this:

event {
  portEvent {
    localPort: 5005
    remotePort: 5005
    podName: "skaffold-spring-boot-56df7ff876-65xf8"
    containerName: "skaffold-spring-boot"
    namespace: "default"
  }
}

In order for clients to distinguish between forwarded application ports vs forwarded debug ports, we should add portName to this event (which is prefixed with a debug identifier). This debug identifier will be added to the portName as part of the skaffold debug PR: #1702