Add a small prompt to the UpdateAllocationTokensCommand

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=248523681

java/google/registry/tools/UpdateAllocationTokensCommand.java

@@ -123,6 +123,11 @@ public final class UpdateAllocationTokensCommand extends ConfirmingCommand
             .collect(toImmutableSet());
   }
 
+  @Override
+  public String prompt() {
+    return String.format("Update %d tokens?", tokensToSave.size());
+  }
+
   @Override
   protected String execute() {
     long numUpdated =