Add a fast mode to the ResaveAllEppResourcesAction mapreduce (#912)

* Add a fast mode to the ResaveAllEppResourcesAction mapreduce

This new mode avoids writing no-op mutations for entities that don't actually
have any changes to write. The cronjobs use fast mode by default, but manual
invocations do not, as manual invocations are often used to trigger @OnLoad
migrations, and fast mode won't pick up on those changes.

core/src/test/java/google/registry/batch/ResaveAllEppResourcesActionTest.java

@@ -55,6 +55,19 @@ class ResaveAllEppResourcesActionTest extends MapreduceTestCase<ResaveAllEppReso
         .isGreaterThan(creationTime);
   }
 
+  @Test
+  void test_fastMode_doesNotResaveEntityWithNoChanges() throws Exception {
+    ContactResource contact = persistActiveContact("test123");
+    DateTime creationTime = contact.getUpdateTimestamp().getTimestamp();
+    assertThat(ofy().load().entity(contact).now().getUpdateTimestamp().getTimestamp())
+        .isEqualTo(creationTime);
+    ofy().clearSessionCache();
+    action.isFast = true;
+    runMapreduce();
+    assertThat(ofy().load().entity(contact).now().getUpdateTimestamp().getTimestamp())
+        .isEqualTo(creationTime);
+  }
+
   @Test
   void test_mapreduceResolvesPendingTransfer() throws Exception {
     DateTime now = DateTime.now(UTC);