Add additional stub methods for FakeApplicationSetting

In a migration spec, a default ApplicationSetting object may fail to
create due to an unknown attribute and fall back to
FakeApplicationSetting.  FakeApplicationSetting appears to be missing a
number of methods that are needed
(https://gitlab.com/gitlab-org/gitlab-ce/issues/47491). This commit adds
the ones needed to make an EE spec pass.

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/7543

lib/gitlab/fake_application_settings.rb

@@ -5,16 +5,6 @@
 # column type without parsing db/schema.rb.
 module Gitlab
   class FakeApplicationSettings < OpenStruct
-    def initialize(options = {})
-      super
-
-      FakeApplicationSettings.define_predicate_methods(options)
-    end
-
-    def pick_repository_storage
-      repository_storages.sample
-    end
-
     # Mimic ActiveRecord predicate methods for boolean values
     def self.define_predicate_methods(options)
       options.each do |key, value|
@@ -27,5 +17,23 @@ module Gitlab
         end
       end
     end
+
+    def initialize(options = {})
+      super
+
+      FakeApplicationSettings.define_predicate_methods(options)
+    end
+
+    def key_restriction_for(type)
+      0
+    end
+
+    def allowed_key_types
+      ApplicationSetting::SUPPORTED_KEY_TYPES
+    end
+
+    def pick_repository_storage
+      repository_storages.sample
+    end
   end
 end