add template preferences

app/controllers/templates_preferences_controller.rb

@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+class TemplatesPreferencesController < ApplicationController
+  load_and_authorize_resource :template
+
+  def show; end
+
+  def create
+    authorize!(:update, @template)
+
+    @template.preferences = @template.preferences.merge(template_params[:preferences])
+    @template.save!
+
+    head :ok
+  end
+
+  private
+
+  def template_params
+    params.require(:template).permit(preferences: %i[bcc_completed request_email_subject request_email_body])
+  end
+end