feat: add marketing email option on registration (#29397)

lms/static/js/student_account/views/RegisterView.js

@@ -86,7 +86,7 @@
                         html.push(HtmlUtils.template(fieldTpl)($.extend(fields[i], {
                             form: this.formType,
                             requiredStr: this.requiredStr,
-                            optionalStr: this.optionalStr,
+                            optionalStr: fields[i].name === 'marketing_emails_opt_in' ? '' : this.optionalStr,
                             supplementalText: fields[i].supplementalText || '',
                             supplementalLink: fields[i].supplementalLink || ''
                         })));

lms/static/sass/views/_login-register.scss

@@ -320,6 +320,12 @@ ul.fa-ul{
       width: calc(50% - 10px);
     }
 
+    &.checkbox-marketing_emails_opt_in {
+      .label-text {
+        font-size: small !important;
+      }
+    }
+
     .label-text-small {
       font-size: small;
     }

lms/templates/student_account/form_field.underscore

@@ -101,6 +101,7 @@
             <% if ( restrictions.max_length && type !== 'password' ) { %> maxlength="<%- restrictions.max_length %>"<% } %>
             <% if ( restrictions.readonly )   { %> readonly <% } %>
             <% if ( required ) { %> required<% } %>
+            <% if ( defaultValue === true ) { %> checked<% } %>
             <% if ( typeof errorMessages !== 'undefined' ) {
                 _.each(errorMessages, function( msg, type ) {%>
                     data-errormsg-<%- type %>="<%- msg %>"