Add missing Kontakt 'enable_unified_mailboxes' needle

The last one of these was deleted during the last needle cleanup,
but we do actually still occasionally hit the dialog, e.g. in
https://openqa.fedoraproject.org/tests/1837435/modules/kontakt/steps/3
so let's add an updated version of the needle.

Signed-off-by: Adam Williamson <awilliam@redhat.com>

needles/kde/apps/enable_unified_mailboxes-20230428.json

@@ -0,0 +1,15 @@
+{
+  "area": [
+    {
+      "xpos": 446,
+      "ypos": 445,
+      "width": 154,
+      "height": 15,
+      "type": "match"
+    }
+  ],
+  "properties": [],
+  "tags": [
+    "enable_unified_mailboxes"
+  ]
+}