Automatize MARGO_REGISTER

We need to register each RPC separately using the macro MARGO_REGISTER, although there is an attemps called rpc_register, it does not support RPCs with input and output parameters.

For each RPC, we should do :

        auto id = MARGO_REGISTER(m_context->m_mid, "ADM_input", ADM_input_in_t, ADM_input_out_t, ADM_input);
        m_context->m_rpc_names.emplace("ADM_input", id);

One option could be to extend MARGO_REGISTER original macro.