Add rate-limiting on queries with Hammer

Closes #67

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/graphql/authorization.ex

@@ -44,6 +44,9 @@ defmodule Mobilizon.GraphQL.Authorization do
   def get_user_role(%{role: role}), do: role
   def get_user_role(nil), do: nil
 
+  @impl true
+  def get_ip(%{ip: ip}), do: ip
+
   @impl true
   def unauthorized_message(resolution) do
     case Map.get(resolution.context, :current_user) do