boolean isExpired() {
      return creationTimestamp < System.currentTimeMillis() - CACHE_VALID_DURATION_IN_MS;
    }
Check if is this entry is expired. The condition for expiry uses {@code creationTimestamp}. This is good enough as
this means that the cached set of fetches entries hasn't been consumed within the invalidation duration.
@return true if this entry is expired. false otherwise.
ambry-cloud/src/main/java/com/github/ambry/cloud/azure/CosmosChangeFeedBasedReplicationFeed.java