Rename custom/conf/app.ini.sample to custom/conf/app.example.ini for better syntax light on editor (#11926)
* Rename custom/conf/app.ini.sample to custom/conf/app.sample.ini for better syntax light on editor
* rename to app.example.ini
* per @6543 's comment, update all references on docs
Co-authored-by: techknowlogick <techknowlogick@gitea.io>