Add additional specific PricingEngineProxy methods

We already had methods to return just the create or just the renew price. I added more to return just the premium flag or just the fee class.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=136833071

javatests/google/registry/flows/domain/TldSpecificLogicProxyTest.java

@@ -84,7 +84,7 @@ public class TldSpecificLogicProxyTest extends ShardableTestCase {
                     b, Money.of(USD, 50)))
             .build());
     basicCreateCost =
-        PricingEngineProxy.getPricesForDomainName("example.tld", clock.nowUtc()).getCreateCost();
+        PricingEngineProxy.getDomainCreateCost("example.tld", clock.nowUtc(), 1);
   }
 
   @Test