configitems: register the 'web.deny_push' config

mercurial/configitems.py

@@ -733,6 +733,9 b" coreconfigitem('web', 'cache',"
 coreconfigitem('web', 'contact',
     default=None,
 )
+coreconfigitem('web', 'deny_push',
+    default=list,
+)
 coreconfigitem('web', 'accesslog',
     default='-',
 )