DEV: Add support for allowed parameters in user api key scopes

Initially, this feature is only intended for use in core/plugins, so there is no API for requesting a parameter-scoped key. That may change in future.

db/migrate/20201008105539_add_allowed_parameters_to_user_api_key_scope.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class AddAllowedParametersToUserApiKeyScope < ActiveRecord::Migration[6.0]
+  def change
+    add_column :user_api_key_scopes, :allowed_parameters, :jsonb
+  end
+end