Add a key to the alloc table on the task group detail page

Adding keys tells Ember to rerender matching entries instead of
destroying and recreating.

Without this key, every time the allocation collection changes, every
allocation row gets destroyed and recreated.

This happens a lot, since each allocation needs to be reloaded which
dirties the collection.

Since allocation rows fetch stats on init, each of these many many
renders results in a stats request.

By using key and rerendering matching records, this all goes away. Since
the rows aren't being destroyed and recreated, the init stats request
isn't being made overnumerously.

ui/app/templates/jobs/job/task-group.hbs

@@ -98,7 +98,7 @@
               <th>CPU</th>
               <th>Memory</th>
             </t.head>
-            <t.body as |row|>
+            <t.body @key="model.id" as |row|>
               <AllocationRow @data-test-allocation={{row.model.id}} @allocation={{row.model}} @context="taskGroup" @onClick={{action "gotoAllocation" row.model}} />
             </t.body>
           </ListTable>