Don't install ReplicationStatusModule when replication lag is disabled

The ReplicationStatusModule is responsible for scanning *all* the
projects and checking their replication lag 'refs/multi-site/version'
against the global-refdb.

If the replication lag isn't enabled, there is no point to run the
expensive job of scanning all repos, saving precious CPU cycles and
avoiding the associated disk I/O and global-refdb calls.

Change-Id: Ib8be7d3fc14cb319d395d6ba676c2254edb1cdf5

src/main/java/com/googlesource/gerrit/plugins/multisite/PluginModule.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/multisite/PluginModule.java b/src/main/java/com/googlesource/gerrit/plugins/multisite/PluginModule.java
index db06c9f..62f38ad 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/multisite/PluginModule.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/multisite/PluginModule.java
@@ -67,7 +67,9 @@
       install(new BrokerForwarderModule());
       listener().to(MultiSiteConsumerRunner.class);
 
-      install(new ReplicationStatusModule(workQueue));
+      if (config.replicationLagEnabled()) {
+        install(new ReplicationStatusModule(workQueue));
+      }
     }
 
     if (config.getSharedRefDbConfiguration().getSharedRefDb().isEnabled()) {