stream settings: Hide creating admin-only streams in members UI.

This commit takes away the ability for non-admin members to create
streams where only admins can post messages by hiding the option from
them.

Fixes #11290.

frontend_tests/node_tests/templates.js

@@ -1230,6 +1230,7 @@ run_test('subscription_stream_privacy_modal', () => {
     var args = {
         stream_id: 999,
         is_private: true,
+        is_admin: true,
     };
     var html = render('subscription_stream_privacy_modal', args);
 

static/js/subs.js

@@ -580,6 +580,7 @@ exports.setup_page = function (callback) {
             hide_all_streams: !should_list_all_streams(),
             max_name_length: page_params.stream_name_max_length,
             max_description_length: page_params.stream_description_max_length,
+            is_admin: page_params.is_admin,
         };
 
         var rendered = templates.render('subscription_table_body', template_data);

static/templates/stream_types.handlebars

@@ -17,6 +17,7 @@
             {{t '<b>Private, protected history:</b> must be invited by a member; new members can only see messages sent after they join; hidden from non-administrator users' }}
         </label>
     </li>
+    {{#if is_admin}}
     <li>
         <label class="checkbox">
             <input type="checkbox" name="is-announcement-only" value="is-announcement-only" {{#if is_announcement_only}}checked{{/if}}/>
@@ -24,4 +25,5 @@
             {{t 'Restrict posting to organization administrators' }}
         </label>
     </li>
+    {{/if}}
 </ul>