Custom configuration for the mix task

In this release, @emilianobovetti fixed an issue with custom configurations for the registration mix task. If you want to use your special config, let's say config/runtime.exs, now you can specify it via --appconfig option, like that

mix avrora.reg.schema --name io.confluent.Payment --appconfig runtime
schema `io.confluent.Payment' will be registered

it will be loaded in addition to the default one (if it's present)

Enjoy! Thanks to @emilianobovetti 💙