Working on "Use std::filesystem. Remove Boost Filesystem & System" #20744, I found an unfortunate [pitfall](https://github.com/bitcoin/bitcoin/pull/20744#issuecomment-946046666) -- `boost/process.hpp` depends on `boost::filesystem` when cross-compiling for Windows. It happens in Guix environment as well.

The goal of this issue is to discuss and find a solution to get rid of `boost::filesystem`.
{
    const util::SettingsValue value = GetSetting(strArg);
    return value.isNull() ? nDefault : value.isFalse() ? 0 : value.isTrue() ? 1 : value.isNum() ? value.get_int64() : LocaleIndependentAtoi<int64_t>(value.get_str());
}
bool ArgsManager::GetBoolArg(const std::string& strArg, bool fDefault) const
{
    const util::SettingsValue value = GetSetting(strArg);
    return value.isNull() ? fDefault : value.isBool() ? value.get_bool() : InterpretBool(value.get_str());
}
bool ArgsManager::SoftSetArg(const std::string& strArg, const std::string& strValue)
{
    LOCK(cs_args);
    if (IsArgSet(strArg)) return false;
    ForceSetArg(strArg, strValue);
    return true;
}
bool ArgsManager::SoftSetBoolArg(const std::string& strArg, bool fValue)
{
    if (fValue)
        return SoftSetArg(strArg, std::string("1"));
    else
        return SoftSetArg(strArg, std::string("0"));
}
void ArgsManager::ForceSetArg(const std::string& strArg, const std::string& strValue)
{
    LOCK(cs_args);
    m_settings.forced_settings[SettingName(strArg)] = strValue;
}
void ArgsManager::AddCommand(const std::string& cmd, const std::string& help)