Add simple feature flag system (#34038)

Co-authored-by: Claire <claire.github-309c@sitedethib.com>

lib/mastodon/feature.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+module Mastodon::Feature
+  class << self
+    def enabled_features
+      @enabled_features ||=
+        (Rails.configuration.x.mastodon.experimental_features || '').split(',').map(&:strip)
+    end
+
+    def method_missing(name)
+      if respond_to_missing?(name)
+        feature = name.to_s.delete_suffix('_enabled?')
+        enabled = enabled_features.include?(feature)
+        define_singleton_method(name) { enabled }
+
+        return enabled
+      end
+
+      super
+    end
+
+    def respond_to_missing?(name)
+      name.to_s.end_with?('_enabled?')
+    end
+  end
+end