configitems: register the 'server.validate' config

mercurial/changegroup.py

@@ -309,7 +309,7 b' class cg1unpacker(object):'
             self._unpackmanifests(repo, revmap, trp, prog, changesets)
 
             needfiles = {}
-            if repo.ui.configbool('server', 'validate', default=False):
+            if repo.ui.configbool('server', 'validate'):
                 cl = repo.changelog
                 ml = repo.manifestlog
                 # validate incoming csets have their manifests

mercurial/configitems.py

@@ -137,6 +137,9 b" coreconfigitem('server', 'preferuncompre"
 coreconfigitem('server', 'uncompressedallowsecret',
     default=False,
 )
+coreconfigitem('server', 'validate',
+    default=False,
+)
 coreconfigitem('ui', 'clonebundleprefers',
     default=list,
 )