Make the default Trigger hibernation 3 minutes instead of 5 seconds

The `min()` vs `max()` fix in D17560 meant that the Trigger daemon only
hibernates for 5 seconds, so we do a full GC sweep every 5 seconds. This ends
up eating a fair amount of CPU for no real benefit.

The GC cursors should move to persistent storage, but just bump this default
up in the meantime.

Auditors: chad

src/infrastructure/daemon/workers/PhabricatorTriggerDaemon.php

@@ -275,7 +275,7 @@ final class PhabricatorTriggerDaemon
    * @return int Number of seconds to sleep for.
    */
   private function getSleepDuration() {
-    $sleep = 5;
+    $sleep = phutil_units('3 minutes in seconds');
 
     $next_triggers = id(new PhabricatorWorkerTriggerQuery())
       ->setViewer($this->getViewer())