Adds sortable prop to columns

app/assets/javascripts/alert_management/components/alert_management_list.vue

@@ -41,34 +41,40 @@ export default {
       key: 'severity',
       label: s__('AlertManagement|Severity'),
       tdClass: `${tdClass} rounded-top text-capitalize`,
+      sortable: true,
     },
     {
       key: 'startedAt',
       label: s__('AlertManagement|Start time'),
       tdClass,
+      sortable: true,
     },
     {
       key: 'endedAt',
       label: s__('AlertManagement|End time'),
       tdClass,
+      sortable: true,
     },
     {
       key: 'title',
       label: s__('AlertManagement|Alert'),
       thClass: 'w-30p',
       tdClass,
+      sortable: true,
     },
     {
       key: 'eventCount',
       label: s__('AlertManagement|Events'),
       thClass: 'text-right gl-pr-9',
       tdClass: `${tdClass} text-md-right`,
+      sortable: true,
     },
     {
       key: 'status',
       thClass: 'w-15p',
       label: s__('AlertManagement|Status'),
       tdClass: `${tdClass} rounded-bottom`,
+      sortable: true,
     },
   ],
   statuses: {