di.xml

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="Magento\Checkout\Block\Checkout\LayoutProcessor">
        <plugin name="add_custom_field_checkout_shipping_form" type="BobGroup\BobGo\Plugin\Checkout\Block\LayoutProcessorPlugin" sortOrder="10"/>
        <arguments>
            <argument name="layoutProcessors" xsi:type="array">
                <item name="orderattribute" xsi:type="object">BobGroup\BobGo\Plugin\Checkout\Block\LayoutProcessorPlugin</item>
            </argument>
        </arguments>
    </type>
</config>