Make AppConfig part of the public API

apps/provisioning_api/appinfo/routes.php

apps/provisioning_api/lib/Controller/AppConfigController.php

core/ajax/appconfig.php

core/js/config.js

core/js/core.json

core/js/js.js

core/js/public/appconfig.js

core/routes.php

core/shipped.json

lib/private/legacy/template.php

settings/js/admin.js

tests/lib/App/ManagerTest.php

tests/lib/AppTest.php