Create tool to extract network snapshot

[nonsense]

Once we hit a bug in a private deployment, we should have a way to extract the network topology, maybe in terms of a snapshot JSON, so that we can reproduce the bug in a test environment with the Simulation framework.

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1. Create a binary that takes the following params (assume that kubectl proxy is running on the local machine, so you can target http://localhost:8001):

./extract_network_topology --namespace=staging --deployment=swarm-private --nodes=30 > snapshot.json

2. You can add the binary under github.com/ethereum/go-ethereum/cmd/swarm/extract_network_topology