Create a command line tool to visualize output of rpc get /network/connections

[itkach]

When working on setting up tezos p2p network it is useful to be able to analyze the topology/connectivity in the resulting network.

Output of tezos rpc /network/connections endpoint is json that describes nodes connections. It lists incoming and outgoing connections to other peers on the network.

Create a tool that generates a graph that represents these connections in graphviz format (dot). It should be able to visualize output of individual node's /network/connections but also crawl the p2p network and aggregate connections info from all nodes into a single graph.