Add classes for using in styles, JS and tests

app/views/projects/protected_tags/_create_protected_tag.html.haml

-= form_for [@project.namespace.becomes(Namespace), @project, @protected_tag] do |f|
+= form_for [@project.namespace.becomes(Namespace), @project, @protected_tag], html: { class: 'new-protected-tag js-new-protected-tag' } do |f|
   .panel.panel-default
     .panel-heading
       %h3.panel-title