func Merge(cfgKVS map[string]KVS, envname string, defaultKVS KVS) map[string]KVS {
	newCfgKVS := make(map[string]KVS)
	for _, e := range env.List(envname) {
		tgt := strings.TrimPrefix(e, envname+Default)
		if tgt == envname {
			tgt = Default
		}
		newCfgKVS[tgt] = defaultKVS
	}
	maps.Copy(newCfgKVS, cfgKVS)
	return newCfgKVS
}

// Set sets a value, if not sets a default value.