Migrate checkbox to use GitLab UI component

app/views/admin/application_settings/_terms.html.haml

-= form_for @application_setting, url: general_admin_application_settings_path(anchor: 'js-terms-settings'), html: { class: 'fieldset-form', id: 'terms-settings' } do |f|
+= gitlab_ui_form_for @application_setting, url: general_admin_application_settings_path(anchor: 'js-terms-settings'), html: { class: 'fieldset-form', id: 'terms-settings' } do |f|
   = form_errors(@application_setting)
 
   %fieldset
     .form-group
-      .form-check
-        = f.check_box :enforce_terms, class: 'form-check-input'
-        = f.label :enforce_terms, class: 'form-check-label' do
-          = _("All users must accept the Terms of Service and Privacy Policy to access GitLab")
-        .form-text.text-muted
+      = f.gitlab_ui_checkbox_component :enforce_terms, _("All users must accept the Terms of Service and Privacy Policy to access GitLab")
     .form-group
       = f.label :terms do
         = _("Terms of Service Agreement and Privacy Policy")