Persist RS auth tokens in Redis

spec/factories/remote_storage_authorizations.rb

@@ -0,0 +1,9 @@
+FactoryBot.define do
+  factory :remote_storage_authorization do
+    permissions { ["documents:rw"] }
+    client_id { "some-fancy-app" }
+    redirect_uri { "https://example.com/some-fancy-app" }
+    app_name { "Fancy App" }
+    expire_at { nil }
+  end
+end