Allow service support to change the significant date

Whilst earlier implementation allowed them to do this, we refactored that
so this work allows them to once again change the conversion or transfer
date on a project.

app/policies/project_policy.rb

@@ -53,6 +53,7 @@ def update?
 
   def change_significant_date?
     return false if @record.significant_date_provisional?
+    return true if @user.is_service_support?
 
     project_assigned_to_user?
   end

spec/policies/project_policy_spec.rb

@@ -55,6 +55,10 @@
         expect(subject).to permit(application_user, build(:conversion_project, assigned_to: application_user, conversion_date_provisional: false))
       end
 
+      it "grants access if the user is service support" do
+        expect(subject).to permit(build(:user, :service_support), build(:conversion_project, assigned_to: application_user, conversion_date_provisional: false))
+      end
+
       it "denies access if the project is assigned to another user" do
         expect(subject).not_to permit(application_user, build(:conversion_project, assigned_to: build(:user), conversion_date_provisional: false))
       end