[skip ci] Refine connection manager comment (#12486)

Signed-off-by: Edward Zeng <jie.zeng@zilliz.com>

internal/distributed/connection_manager.go

@@ -70,6 +70,7 @@ type ConnectionManager struct {
 	closeCh chan struct{}
 }
 
+// NewConnectionManager creates a new connection manager.
 func NewConnectionManager(session *sessionutil.Session) *ConnectionManager {
 	return &ConnectionManager{
 		session: session,