add `SocketProxy` support

[shadeofblue]

Why:

• enable direct access to tcp services hosted inside dapps (eg db)

What:

• add support to the descriptor and to the runner code
• update the GAP golemfactory/golem-architecture#39

[shadeofblue]

proposed solution:

nodes:
  db:
    payload: "db"
    init:
      - run:
          args:
            - "/bin/run_rqlite.sh"
    tcp_proxy:
      ports:
        - "4001" 
    network: "default"
    ip:
      - "192.168.0.2"
  http:
    payload: "http"
    init:
      - run:
          args: ["/bin/bash", "-c", "cd /webapp && python app.py --db-address 192.168.0.2 --db-port 4001 initdb"]
      - run:
          args: ["/bin/bash", "-c", "cd /webapp && python app.py --db-address 192.168.0.2 --db-port 4001 run > /webapp/out 2> /webapp/err &"]
    http_proxy:
      ports:
        - "5000"  # specify just the remote port, allow the local port to be automatically chosen
    network: "default"
    ip:
      - "192.168.0.3"
    depends_on:
      - "db"

[shadeofblue]

or maybe it should be expose instead of proxy ?

[stranger80]

can we call it tcp_proxy to be more precise?

[shadeofblue]

-> golemfactory/golem-architecture#62