Make the verify OT&E action more performant

As previously written, it loaded up all history entries into memory and then
processed them. This was OOMing for some registrars on sandbox who had performed
a large number of testing actions, most of them long OT&E was passed.

This commit changes the verify OT&E action to stream the history entries in
batches, ordered by when they were made, and then terminates once all tests have
passed. This prevents OOMing because only a single batch of history entries need
reside in memory at once.

This does necessitate the creation of a new composite Datastore index on
HistoryEntry, so we'll need to run the ResaveAllHistoryEntriesAction in sandbox
after this change is deployed before the new verify OT&E code will work.

Note that the "history viewer" is long dead, but that the pre-existing index
on HistoryEntries is still used for many other purposes.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=223163337

java/google/registry/env/common/default/WEB-INF/datastore-indexes.xml

@@ -69,10 +69,14 @@
     <property name="clientId" direction="asc"/>
     <property name="eventTime" direction="asc"/>
   </datastore-index>
-  <!-- For the history viewer. -->
+  <!-- For querying HistoryEntries. -->
   <datastore-index kind="HistoryEntry" ancestor="true" source="manual">
     <property name="modificationTime" direction="asc"/>
   </datastore-index>
+  <datastore-index kind="HistoryEntry" ancestor="false" source="manual">
+    <property name="clientId" direction="asc"/>
+    <property name="modificationTime" direction="asc"/>
+  </datastore-index>
   <!-- For RDAP. -->
   <datastore-index kind="DomainBase" ancestor="false" source="manual">
     <property name="^i" direction="asc"/>