Add beta/dev gateway tag to webapp eip-service.json

Currently, this is what eip-service.json shows per gateway:

$ curl -k https://api.black.riseup.net/1/config/eip-service.json
{
  "gateways": [
    {
      "capabilities": {
        "adblock": false,
        "filter_dns": false,
        "limited": false,
        "ports": [
          "443"
        ],
        "protocols": [
          "tcp"
        ],
        "transport": [
          "openvpn"
        ],
        "user_ips": false
      },
      "host": "cisne.riseup.net",
      "ip_address": "37.218.241.7",
      "location": "miami"
    },
…

We should add a "dev" or "beta" boolean tag to each gw.