Add getPushBatchSize implementation

The getPushBatchSize has been introduced in the replication
plugin with commit 756d349c

Pull replication needs to adhere to the new interface.

Change-Id: I6d7051415ee78225678adca6c28975ea68621581

src/main/java/com/googlesource/gerrit/plugins/replication/pull/SourceConfiguration.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/pull/SourceConfiguration.java b/src/main/java/com/googlesource/gerrit/plugins/replication/pull/SourceConfiguration.java
index 4858b17..b6cbaa4 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/pull/SourceConfiguration.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/pull/SourceConfiguration.java
@@ -205,4 +205,9 @@
   public int getSlowLatencyThreshold() {
     return slowLatencyThreshold;
   }
+
+  @Override
+  public int getPushBatchSize() {
+    return 0;
+  }
 }