Modify _configsvrAddShard() to include a notification on its completion to a remote shard node

When an addShard() command gets committed by the config server, the event should be registered in the oplog of other shards of the cluster to ensure that mongos processes will eventually be notified.

The objective of this ticket is to ensure that _configsvrAddShard() includes a successful invocation of the command introduced in SERVER-71754 as part of its commit section.