Restatectl becomes slow if multiple nodes are unreachable

[tillrohrmann]

When running restatectl to fetch information from a cluster where nodes are down, the output takes a long time to be printed. I think it might be caused by awaiting timeouts for network requests sequentially. Maybe we can prevent a linear increase in the output delay by running the network requests in parallel instead of sequentially. Maybe we can also show some indicator in the cli that it is still fetching the information (some kind of progress indicator).