This ticket should also add the showSystemEvents flag.

There are also two existing flags with similar semantics:

• The allowToRunOnConfigDb will allow opening a change stream on the config database (which is on the config servers) through mongos.
• And the allowToRunOnSystemNamespace will let the users run the change stream on the system collection

We need to ensure that even if the existing flags are turned off, enabling showSystemEvents is still enough to show system events.