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/export/ExportSnapshotAction.java

@@ -20,6 +20,7 @@ import static google.registry.request.Action.Method.POST;
 import google.registry.config.RegistryConfig;
 import google.registry.request.Action;
 import google.registry.request.Response;
+import google.registry.request.auth.Auth;
 import google.registry.util.Clock;
 import google.registry.util.FormattingLogger;
 import javax.inject.Inject;
@@ -37,7 +38,12 @@ import javax.inject.Inject;
  *   <li>The {@link UpdateSnapshotViewAction} updates the view in latest_snapshot.
  * </ol>
  */
-@Action(path = ExportSnapshotAction.PATH, method = POST, automaticallyPrintOk = true)
+@Action(
+  path = ExportSnapshotAction.PATH,
+  method = POST,
+  automaticallyPrintOk = true,
+  auth = Auth.AUTH_INTERNAL_ONLY
+)
 public class ExportSnapshotAction implements Runnable {
 
   /** Queue to use for enqueuing the task that will actually launch the backup. */