Set EAP billing event to one-year period

This is consistent with how we treat RESTORE billing events as well- in
general, fees are considered to be amortized over the course of a year (by the
invoicing team).

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=199684843

java/google/registry/flows/domain/DomainCreateFlow.java

@@ -525,6 +525,7 @@ public class DomainCreateFlow implements TransactionalFlow {
         .setReason(Reason.FEE_EARLY_ACCESS)
         .setTargetId(createBillingEvent.getTargetId())
         .setClientId(createBillingEvent.getClientId())
+        .setPeriodYears(1)
         .setCost(feesAndCredits.getEapCost())
         .setEventTime(createBillingEvent.getEventTime())
         .setBillingTime(createBillingEvent.getBillingTime())

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

@@ -304,13 +304,14 @@ public abstract class BillingEvent extends ImmutableObject
         ImmutableSet<Reason> reasonsWithPeriods =
             Sets.immutableEnumSet(
                 Reason.CREATE,
+                Reason.FEE_EARLY_ACCESS,
                 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, RESTORE or TRANSFER.");
+                + "CREATE, FEE_EARLY_ACCESS, RENEW, RESTORE or TRANSFER.");
         checkState(
             instance.getFlags().contains(Flag.SYNTHETIC)
                 == (instance.syntheticCreationTime != null),