Change @Auth to an AutoValue, and created a set of predefined Auths

We want to be safer and more explicit about the authentication needed by the many actions that exist.

As such, we make the 'auth' parameter required in @Action (so it's always clear who can run a specific action) and we replace the @Auth with an enum so that only pre-approved configurations that are aptly named and documented can be used.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=162210306

java/google/registry/cron/CommitLogFanoutAction.java

@@ -23,12 +23,17 @@ import com.google.common.base.Optional;
 import google.registry.model.ofy.CommitLogBucket;
 import google.registry.request.Action;
 import google.registry.request.Parameter;
+import google.registry.request.auth.Auth;
 import google.registry.util.TaskEnqueuer;
 import java.util.Random;
 import javax.inject.Inject;
 
 /** Action for fanning out cron tasks for each commit log bucket. */
-@Action(path = "/_dr/cron/commitLogFanout", automaticallyPrintOk = true)
+@Action(
+  path = "/_dr/cron/commitLogFanout",
+  automaticallyPrintOk = true,
+  auth = Auth.AUTH_INTERNAL_ONLY
+)
 public final class CommitLogFanoutAction implements Runnable {
 
   public static final String BUCKET_PARAM = "bucket";