Create and list Avis on Dossier detail page

app/controllers/backoffice/avis_controller.rb

@@ -0,0 +1,21 @@
+class Backoffice::AvisController < ApplicationController
+
+  def create
+    avis = Avis.new(create_params)
+    avis.dossier = dossier
+    avis.save
+
+    redirect_to backoffice_dossier_path(dossier)
+  end
+
+  private
+
+  def dossier
+    current_gestionnaire.dossiers.find(params[:dossier_id])
+  end
+
+  def create_params
+    params.require(:avis).permit(:email, :introduction)
+  end
+
+end