URL for sprites is hardcoded

[SimFre]

Hosting a personal copy of the alttpr site is a bit tricky when the URL to the sprites are hardcoded in SettingsController, rather than using a configuration option. Perhaps this should be part of .env? See: https://github.com/sporchia/alttp_vt_randomizer/blob/c602322bbb1f0bd7d8154b2ba4757f009623ed03/app/Http/Controllers/SettingsController.php#L222C1-L222C87

[sporchia]

If you'd like to make a PR adding an ENV var and config option for it we can look to merge it.