Change RESTORE BillingEvents to have 1-year periods

This simplifies calculating the overall invoice by giving RESTORE fees a
period equal to the period of the associated RENEW (1 year). Older
BillingEvents will not be backfilled, and will have periodYears = null.

Invoicing and business both agree this is a valid representation, since RESTORE fees are intrinsically tied to the 1-year RENEW it's associated with.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=188041777

java/google/registry/flows/domain/DomainRestoreRequestFlow.java

@@ -239,7 +239,6 @@ public final class DomainRestoreRequestFlow implements TransactionalFlow  {
   private OneTime createRenewBillingEvent(
       HistoryEntry historyEntry, Money renewCost, DateTime now) {
     return prepareBillingEvent(historyEntry, renewCost, now)
-        .setPeriodYears(1)
         .setReason(Reason.RENEW)
         .build();
   }
@@ -257,6 +256,7 @@ public final class DomainRestoreRequestFlow implements TransactionalFlow  {
         .setClientId(clientId)
         .setEventTime(now)
         .setBillingTime(now)
+        .setPeriodYears(1)
         .setCost(cost)
         .setParent(historyEntry);
   }

java/google/registry/model/billing/BillingEvent.java

@@ -305,10 +305,12 @@ public abstract class BillingEvent extends ImmutableObject
             Sets.immutableEnumSet(
                 Reason.CREATE,
                 Reason.RENEW,
+                Reason.RESTORE,
                 Reason.TRANSFER);
         checkState(
             reasonsWithPeriods.contains(instance.reason) == (instance.periodYears != null),
-            "Period years must be set if and only if reason is CREATE, RENEW, or TRANSFER.");
+            "Period years must be set if and only if reason is "
+                + "CREATE, RENEW, RESTORE or TRANSFER.");
         checkState(
             instance.getFlags().contains(Flag.SYNTHETIC)
                 == (instance.syntheticCreationTime != null),

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

@@ -183,6 +183,7 @@ public class DomainRestoreRequestFlowTest
             .setTargetId("example.tld")
             .setClientId("TheRegistrar")
             .setCost(Money.of(USD, 17))
+            .setPeriodYears(1)
             .setEventTime(clock.nowUtc())
             .setBillingTime(clock.nowUtc())
             .setParent(historyEntryDomainRestore)