HPCC-32934 Capture and report starting timings for ExternalActivity

Signed-off-by: Shamser Ahmed <[email protected]>

thorlcr/activities/external/thexternalslave.cpp

@@ -79,6 +79,7 @@ class CExternalSlaveActivity : public CSlaveActivity
     }
     virtual void start() override
     {
+        ActivityTimer t(slaveTimerStats, timeActivities);
         //Cannot call base base start because that will error if > 1 input
         startAllInputs();
         dataLinkStart();