Show consumer count column on Mgmt UI Channels page

Consumer count is already returned by the /channels API endpoint. Now
the consumer count column can be shown in the channels table but it is
hidden by default.

deps/rabbitmq_management/priv/www/js/global.js

@@ -96,6 +96,7 @@ var ALL_COLUMNS =
                    ['mode',  'Mode',      true],
                    ['state', 'State',     true]],
       'Details': [['msgs-unconfirmed', 'Unconfirmed', true],
+                  ['consumer-count',   'Consumer count', false],
                   ['prefetch',         'Prefetch',    true],
                   ['msgs-unacked',     'Unacked',     true]],
       'Transactions': [['msgs-uncommitted', 'Msgs uncommitted', false],

deps/rabbitmq_management/priv/www/js/tmpl/channels-list.ejs

@@ -35,6 +35,9 @@
 <% if (show_column('channels', 'msgs-unconfirmed')) { %>
     <th><%= fmt_sort('Unconfirmed',     'messages_unconfirmed') %></th>
 <% } %>
+<% if (show_column('channels', 'consumer-count')) { %>
+    <th><%= fmt_sort('Consumer count', 'consumer_count') %></th>
+<% } %>
 <% if (show_column('channels', 'prefetch')) { %>
     <th>Prefetch <span class="help" id="channel-prefetch"></span></th>
 <% } %>
@@ -85,6 +88,9 @@
 <% if (show_column('channels', 'msgs-unconfirmed')) { %>
     <th>Unconfirmed</th>
 <% } %>
+<% if (show_column('channels', 'consumer-count')) { %>
+    <th>Consumer count</th>
+<% } %>
 <% if (show_column('channels', 'prefetch')) { %>
     <th>Prefetch <span class="help" id="channel-prefetch"></span></th>
 <% } %>
@@ -152,6 +158,9 @@
 <% if (show_column('channels', 'msgs-unconfirmed')) { %>
     <td class="c"><%= channel.messages_unconfirmed %></td>
 <% } %>
+<% if (show_column('channels', 'consumer-count')) { %>
+    <td class="c"><%= channel.consumer_count %></td>
+<% } %>
 <% if (show_column('channels', 'prefetch')) { %>
     <td class="c">
       <% if (channel.prefetch_count != 0) { %>