improve `/health` endpoint informations

[mrpalide]

Fix: #19

Changes:

• add dmsg_servers info to /health endpoint of AR, RF, and TPD
• update dmsg to develop

How to test:

• clone skywire at develop, and skywire-services, skywire-ut, skycoin-service-discovery and dmsg at related branch to this PR
• run integration test env by make integration-env-build
• check /health endpoints of services at:
  • http://dmsg-discovery:9090/health
  • http://transport-discovery:9091/health
  • http://route-finder:9092/health
  • http://address-resolver:9093/health
  • http://uptime-tracker:9096/health
  • http://service-discovery:9098/health

Note: dmsg-discovery needs 1 minute wait for test, at the beginning no dmsg-server available there.