MM-13015 Add safety valve setting to disable post metadata (#9877)

* MM-13015 Add safety valve setting to disable post metadata

* Remove setting from client config since it's no longer needed

config/default.json

@@ -360,7 +360,8 @@
     },
     "ExperimentalSettings": {
         "ClientSideCertEnable": false,
-        "ClientSideCertCheck": "secondary"
+        "ClientSideCertCheck": "secondary",
+        "DisablePostMetadata": false
     },
     "AnalyticsSettings": {
         "MaxUsersForStatistics": 2500