Make async flow logic handle missing client transaction IDs

Per EPP RFC 5730, the <clTRID> element is optional. However, we weren't handling
it not being specified in asynchronous contact/host deletions because we were
adding it directly as a parameter value on a task, which does not allow null and
thus threw a NullPointerException.

This fixes handling for nulls (the parameter isn't set at all) and adds a test.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=194123259

java/google/registry/tools/GetHistoryEntriesCommand.java

@@ -77,7 +77,7 @@ final class GetHistoryEntriesCommand implements RemoteApiCommand {
           "Client: %s\nTime: %s\nClient TRID: %s\nServer TRID: %s\n%s\n",
           entry.getClientId(),
           entry.getModificationTime(),
-          (entry.getTrid() == null) ? null : entry.getTrid().getClientTransactionId(),
+          (entry.getTrid() == null) ? null : entry.getTrid().getClientTransactionId().orElse(null),
           (entry.getTrid() == null) ? null : entry.getTrid().getServerTransactionId(),
           entry.getXmlBytes() == null
               ? String.format("[no XML stored for %s]\n", entry.getType())