mongos's FTDC had been collecting connPoolStats for some time to track the networking activity on the egress side.

This patch adds these metrics to mongod as well, which may be helpful in diagnosing issues with shard-to-shard communication.

The linked follow-up ticket will add some metrics tracking search-related communication to mongot.

Description of Linked Ticket

Refactor networking collectors into a separate module

This PR extracts the networking-related FTDC collectors from ftdc_mongos.cpp into a new module (networking_collectors.

) and adds them to mongod as well. This allows both mongod and mongos to collect the same networking metrics.

The refactored code includes:

• ConnPoolStatsCollector for connection pool statistics
• NetworkInterfaceStatsCollector for network interface metrics

This change will provide better visibility into networking performance across both mongod and mongos instances.