api: Optmize the number of queries for events

We were fetching event.name for every entry of list, but event.name can
be part of the initial select to retrieve the list of events to
serialize.

This brings the number of queries from 22 to 2 (which makes sense since
we default to retrieving 20 entries).

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>

patchwork/views/api.py

@@ -167,7 +167,7 @@ class EventLogViewSet(mixins.ListModelMixin,
                       ListMixin,
                       viewsets.GenericViewSet):
     permission_classes = (MaintainerPermission, )
-    queryset = EventLog.objects.all()
+    queryset = EventLog.objects.all().select_related('event')
     serializer_class = EventLogSerializer
     filter_backends = (filters.DjangoFilterBackend,)
     filter_class = EventTimeFilter