This adds experimental file filters which are not guaranteed under our stability policies. These filters take effect after reading the files and before parsing their content.
This commit replaces github.com/spf13/viper with github.com/knadh/koanf. Koanf is very similar library to viper, with less dependencies and several quality of life differences. This also allows most config options to be defined by ENV. Lastly it also enables the use of split configuration files which can be configured by setting the --config flag multiple times.
Co-authored-by: Amir Zarrinkafsh <nightah@me.com>