add federation REST API, only stubs (#4056)

scripts/lua/rest/v1/get/federation/data.lua

@@ -0,0 +1,30 @@
+--
+-- (C) 2020 - ntop.org
+--
+
+local dirs = ntop.getDirs()
+package.path = dirs.installdir .. "/scripts/lua/modules/?.lua;" .. package.path
+
+require "lua_utils"
+local json          = require("dkjson")
+local rest_utils    = require("rest_utils")
+local tracker       = require("tracker")
+
+local rc = rest_utils.consts.success.ok
+local res = {}
+
+if not haveAdminPrivileges() then
+   rest_utils.answer(rest_utils.consts.err.not_granted, res)
+   return
+end
+
+-- TODO: collect real statistics about the running ntopng instance
+res = {
+    total_traffic = {up = 100, down = 100},
+    host_number = 10,
+    flow_number = 20,
+    alert_number = 300,
+    version = "v1"
+}
+
+rest_utils.answer(rc, res)