Start dual running with "areas" and "names"

For the public API we actually receive a "name" instead of an ID,
which we also want to start sending from the Admin app.

Unlike IDs, which aren't really used anywhere, we want the names
to display the alerts on gov.uk/alerts.

app/v2/broadcast/post_broadcast.py

@@ -70,6 +70,9 @@ def create_broadcast():
             'areas': [
                 area['name'] for area in broadcast_json['areas']
             ],
+            'names': [
+                area['name'] for area in broadcast_json['areas']
+            ],
             'simple_polygons': polygons.smooth.simplify.as_coordinate_pairs_long_lat,
         },
         status=BroadcastStatusType.PENDING_APPROVAL,

tests/app/v2/broadcast/test_post_broadcast.py

@@ -88,7 +88,7 @@ def test_valid_post_cap_xml_broadcast_returns_201(
     assert response_json['areas'] == [
         'River Steeping in Wainfleet All Saints'
     ]
-    assert response_json['areas_2']['areas'] == [
+    assert response_json['areas_2']['names'] == [
         'River Steeping in Wainfleet All Saints'
     ]
     assert response_json['cancelled_at'] is None