Add REMOVE_OLD_CONFIGS

Enhancement Type

Improve an existing feature

Describe the enhancement

It would be awesome if you could implement env var REMOVE_OLD_CONFIGS.

Aim is to delete/cleanup all files in config folder on server boot before it downloads the modpack.

Why do I need this?

Because some mod authors have designed their mod configs badly and have put client and server configurations in single file. Due to that, so that every modpack update wouldn't override client's custom settings, I've moved some of those settings to defaultoptions configs (which are only copied using some specific mods when the file doesn't already exist).