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`.
break;
            case OptionsCategory::NODE_RELAY:
                usage += HelpMessageGroup("Node relay options:");
                break;
            case OptionsCategory::BLOCK_CREATION:
                usage += HelpMessageGroup("Block creation options:");
                break;
            case OptionsCategory::RPC:
                usage += HelpMessageGroup("RPC server options:");
                break;
            case OptionsCategory::WALLET:
                usage += HelpMessageGroup("Wallet options:");
                break;
            case OptionsCategory::WALLET_DEBUG_TEST:
                if (show_debug) usage += HelpMessageGroup("Wallet debugging/testing options:");
                break;
            case OptionsCategory::CHAINPARAMS:
                usage += HelpMessageGroup("Chain selection options:");
                break;
            case OptionsCategory::GUI:
                usage += HelpMessageGroup("UI Options:");
                break;
            case OptionsCategory::COMMANDS:
                usage += HelpMessageGroup("Commands:");
                break;
            case OptionsCategory::REGISTER_COMMANDS:
                usage += HelpMessageGroup("Register Commands:");
                break;
            default:
                break;