Document dependency from account deactivator to autoUpdateAccountActiveStatus

There was a non-obvious dependency from the AccountDeactivator task to
the auth.autoUpdateAccountActiveStatus. A properly configured account
deactivator task wouldn't be scheduled if the
autoUpdateAccountActiveStatus was set to false and the reason wasn't
obvious to a Gerrit admin.

Also log a warning if the account deactivation task is configured but
will not be scheduled.

Change-Id: Icf13c1b306c52c815438c01d23aa38df0ba30793

Documentation/config-gerrit.txt

@@ -5059,6 +5059,10 @@ account deactivations.
 The link:#schedule-configuration-interval[interval] for running
 account deactivations.
 
+Note that the task will only be scheduled if the
+link:#autoUpdateAccountActiveStatus[auth.autoUpdateAccountActiveStatus]
+is set to true.
+
 link:#schedule-configuration-examples[Schedule examples] can be found
 in the link:#schedule-configuration[Schedule Configuration] section.
 

java/com/google/gerrit/server/account/AccountDeactivator.java

@@ -57,10 +57,14 @@ public class AccountDeactivator implements Runnable {
 
     @Override
     public void start() {
-      if (!supportAutomaticAccountActivityUpdate) {
-        return;
+      if (schedule.isPresent()) {
+        if (supportAutomaticAccountActivityUpdate) {
+          queue.scheduleAtFixedRate(deactivator, schedule.get());
+        } else {
+          logger.atWarning().log(
+              "Not scheduling AccountDeactivator because auth.autoUpdateAccountActiveStatus is false");
+        }
       }
-      schedule.ifPresent(s -> queue.scheduleAtFixedRate(deactivator, s));
     }
 
     @Override