feat: expose system metrics (#4)

Use prom_ex to expose system metrics to prometheus and create dashboards.

Co-authored-by: Joao P Dubas <joao.dubas@gmail.com>
Reviewed-on: #4

lib/wabanex_web/endpoint.ex

@@ -16,6 +16,8 @@ defmodule WabanexWeb.Endpoint do
 
   socket "/live", Phoenix.LiveView.Socket, websocket: [connect_info: [session: @session_options]]
 
+  plug PromEx.Plug, prom_ex_module: Wabanex.PromEx
+
   # Serve at "/" the static files from "priv/static" directory.
   #
   # You should set gzip to true if you are running phx.digest