Add server rules (#15769)

app/controllers/api/v1/instances/rules_controller.rb

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+class Api::V1::Instances::RulesController < Api::BaseController
+  skip_before_action :require_authenticated_user!, unless: :whitelist_mode?
+
+  before_action :set_rules
+
+  def index
+    render json: @rules, each_serializer: REST::RuleSerializer
+  end
+
+  private
+
+  def set_rules
+    @rules = Rule.ordered
+  end
+end