Add extensible custom logic to the domain renew flow

This also adds a TODO in DomainCheckFlow to document the fact that as-of date is not overridden when passed to the custom logic.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=140031318

java/google/registry/flows/domain/DomainCheckFlow.java

@@ -141,6 +141,7 @@ public final class DomainCheckFlow implements Flow {
     customLogic.afterValidation(
         DomainCheckFlowCustomLogic.AfterValidationParameters.newBuilder()
             .setDomainNames(domainNames)
+            // TODO: Use as of date from fee extension v0.12 instead of now, if specificed.
             .setAsOfDate(now)
             .build());
     Set<String> existingIds = checkResourcesExist(DomainResource.class, targetIds, now);