Support reading in registries-config via env (#1199)

Fixes #1198

Author: padlar

cmd/util/config/config.go

@@ -42,6 +42,7 @@ func InitViperWithConfigFile(cfgViper *viper.Viper, configFile string) error {
 	// viper for the general config (file, env and non pre-processed flags)
 	cfgViper.SetEnvPrefix("K3D")
 	cfgViper.AutomaticEnv()
+	cfgViper.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))
 
 	cfgViper.SetConfigType("yaml")