Add customizable user roles (#18641)

* Add customizable user roles

* Various fixes and improvements

* Add migration for old settings and fix tootctl role management

spec/controllers/admin/settings_controller_spec.rb

@@ -7,7 +7,7 @@ RSpec.describe Admin::SettingsController, type: :controller do
 
   describe 'When signed in as an admin' do
     before do
-      sign_in Fabricate(:user, admin: true), scope: :user
+      sign_in Fabricate(:user, role: UserRole.find_by(name: 'Admin')), scope: :user
     end
 
     describe 'GET #edit' do