Currently, ShardingConnectionHook only attaches the reply metadata readers of its egressHook if _shardedConnections is true. For Global Point in Time reads, we want all connections from mongos to check for a "lastCommittedOpTime" field in responses, so we will need to allow for attaching some reply metadata hooks for unsharded connections as well, in particular those from the global connection pool.

Notably the replica set monitor currently uses a ScopedDBConnection to send isMaster commands, which uses unsharded connections from the globalConnPool, and it is important to the GPITR design that these commands track lastCommittedOpTimes.