add ability to reset custom template emails to default

app/controllers/templates_preferences_controller.rb

@@ -3,6 +3,13 @@
 class TemplatesPreferencesController < ApplicationController
   load_and_authorize_resource :template
 
+  RESETTABLE_PREFERENCE_KEYS = {
+    AccountConfig::SUBMITTER_INVITATION_EMAIL_KEY => %w[request_email_subject request_email_body submitters],
+    AccountConfig::SUBMITTER_DOCUMENTS_COPY_EMAIL_KEY => %w[documents_copy_email_subject documents_copy_email_body],
+    AccountConfig::SUBMITTER_COMPLETED_EMAIL_KEY => %w[completed_notification_email_subject
+                                                       completed_notification_email_body]
+  }.freeze
+
   def show; end
 
   def create
@@ -15,6 +22,25 @@ class TemplatesPreferencesController < ApplicationController
     head :ok
   end
 
+  def destroy
+    authorize!(:update, @template)
+
+    config_key = params[:config_key]
+    preferences_to_delete = RESETTABLE_PREFERENCE_KEYS[config_key] || []
+
+    return head :ok if preferences_to_delete.blank?
+
+    preferences_to_delete.each do |key|
+      @template.preferences.delete(key)
+    end
+
+    @template.save!
+
+    render turbo_stream: turbo_stream.replace("#{config_key}_form",
+                                              partial: "templates_preferences/#{config_key}_form"),
+           status: :ok
+  end
+
   private
 
   def template_params