Fully reset domain-list page on registrar change (#2456)

When the registrar changes we should reset the page and the total
results to 0 (since we haven't loaded them yet)

https://b.corp.google.com/issues/343193698

core/src/test/java/google/registry/server/Fixture.java

@@ -154,6 +154,13 @@ public enum Fixture {
                       persistActiveHost("ns5.linode.com").createVKey()))
               .build());
 
+      persistResource(
+          DatabaseHelper.newDomain("newregistrar.example")
+              .asBuilder()
+              .setPersistedCurrentSponsorRegistrarId("NewRegistrar")
+              .setCreationRegistrarId("NewRegistrar")
+              .build());
+
       persistResource(
           loadRegistrar("TheRegistrar")
               .asBuilder()