This PR fixes the missing stat update for `total_net_repl_output_bytes`
that was removed during the refactoring in PR #758. The metric was not
being updated when writing to replica connections.
Changes:
- Restored the stat update in postWriteToClient for replica connections
- Added integration test to verify the metric is properly updated
Signed-off-by: Uri Yagelnik <uriy@amazon.com>
Co-authored-by: Binbin <binloveplay1314@qq.com>