DEV: Enable and fix the 'require-iframe-title' lint

.template-lintrc.js

@@ -31,6 +31,7 @@ module.exports = {
     "no-unnecessary-component-helper": true,
     "no-unused-block-params": true,
     "no-unbound": true,
+    "require-iframe-title": true,
     "self-closing-void-elements": true,
     "simple-unless": true,
     "style-concatenation": true,

app/assets/javascripts/admin/templates/email-preview-digest.hbs

@@ -50,7 +50,7 @@
         {{#if htmlEmpty}}
           <p>{{i18n 'admin.email.no_result'}}</p>
         {{else}}
-          <iframe srcdoc={{model.html_content}} />
+          <iframe title={{i18n 'admin.email.html_preview'}} srcdoc={{model.html_content}} />
         {{/if}}
       {{else}}
         <pre>{{html-safe model.text_content}}</pre>

config/locales/client.en.yml

@@ -3907,6 +3907,7 @@ en:
         format: "Format"
         html: "html"
         text: "text"
+        html_preview: "Email Content Preview"
         last_seen_user: "Last Seen User:"
         no_result: "No results found for summary."
         reply_key: "Reply Key"