p2p, api: add api to return information about your peers

[dshulyak]

add an api endpoint that will return list of peers from host.Network().Peers() and additionally provide information if that peers has a special role (such as bootnode or direct peer). in future we can collect interesting stats about peers and add that to the same endpoint, so format should allow to extend it without significant pain in future

one option is below

[{
  "id": "...",
  "addresses": "...",
  "uptime": "99h", // or maybe connection timestamp
  "tag": ["bootnode", "direct"] 
}]