[#1421] Subject linked dropdown field to feature toggle

app/helpers/type_de_champ_helper.rb

@@ -1,7 +1,8 @@
 module TypeDeChampHelper
   TOGGLES = {
     'piece_justificative' => :champ_pj?,
-    'siret' => :champ_siret?
+    'siret' => :champ_siret?,
+    'linked_drop_down_list' => :champ_linked_dropdown?
   }
 
   def tdc_options

config/features.rb

@@ -11,6 +11,8 @@ Flipflop.configure do
       title: "Champ pièce justificative"
     feature :champ_siret,
       title: "Champ SIRET"
+    feature :champ_linked_dropdown,
+      title: "Champ double menu déroulant"
   end
 
   feature :web_hook