Add nomulus count_domains command

This efficiently counts domains without having to load them (as opposed to the
existing list_domains command which does load then).

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=194559095

java/google/registry/tools/RegistryToolComponent.java

@@ -75,6 +75,7 @@ import javax.inject.Singleton;
   }
 )
 interface RegistryToolComponent {
+  void inject(CountDomainsCommand command);
   void inject(CreateAnchorTenantCommand command);
   void inject(CreateCdnsTld command);
   void inject(CreateContactCommand command);