link to submission preview page in completed emails

app/controllers/submissions_preview_controller.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+class SubmissionsPreviewController < ApplicationController
+  skip_before_action :authenticate_user!
+  skip_authorization_check
+
+  PRELOAD_ALL_PAGES_AMOUNT = 200
+
+  def show
+    @submission = Submission.find_by!(slug: params[:slug])
+
+    ActiveRecord::Associations::Preloader.new(
+      records: [@submission],
+      associations: [:template, { template_schema_documents: :blob }]
+    ).call
+
+    total_pages =
+      @submission.template_schema_documents.sum { |e| e.metadata.dig('pdf', 'number_of_pages').to_i }
+
+    if total_pages < PRELOAD_ALL_PAGES_AMOUNT
+      ActiveRecord::Associations::Preloader.new(
+        records: @submission.template_schema_documents,
+        associations: [:blob, { preview_images_attachments: :blob }]
+      ).call
+    end
+
+    render 'submissions/show', layout: 'plain'
+  end
+end