Add a 1-hour expiration to all Objectify memcache uses

This protects us from the edge case of potentially stale
memcache data due to a DeadlineExceededExeption, or possibly
from MemcacheServiceException. If memcache gets stale and
misses a write that went to Datastore, it will catch up in
at most one hour.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=116174023

java/com/google/domain/registry/model/ofy/Ofy.java

@@ -68,6 +68,15 @@ public class Ofy {
 
   private static final FormattingLogger logger = FormattingLogger.getLoggerForCallerClass();
 
+  /**
+   * Recommended memcache expiration time, which is one hour, specified in seconds.
+   * <p>
+   * This value should used as a cache expiration time for any entities annotated with an Objectify
+   * {@code @Cache} annotation, to put an upper bound on unlikely-but-possible divergence between
+   * memcache and datastore when a memcache write fails.
+   */
+  public static final int RECOMMENDED_MEMCACHE_EXPIRATION = 3600;
+
   /** Default clock for transactions that don't provide one. */
   @NonFinalForTesting
   static Clock clock = new SystemClock();