Magento2 : Add Custom Store Configuration exposed to graphQL

di.xml

<!-- etc/graphql/di.xml -->
<?xml version="1.0"?>

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="Magento\StoreGraphQl\Model\Resolver\Store\StoreConfigDataProvider">
        <arguments>
            <argument name="extendedConfigData" xsi:type="array">
                <item name="custom_config" xsi:type="string">mynamespace_mymodule/general/custom_config</item>
            </argument>
        </arguments>
    </type>
</config>

schema.graphqls

# etc/schema.graphqls

type StoreConfig {
    custom_config : Boolean @doc(description: "Custom Config")
}

system.xml

<!-- etc/adminhtml/system.xml -->
<?xml version="1.0" encoding="UTF-8" ?>

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Config:etc/system_file.xsd">
    <system>
        <tab id="customtab" translate="label" sortOrder="100">
            <label>Custom Tab</label>
        </tab>
        <section id="mynamespace_mymodule" translate="label" sortOrder="100" showInDefault="1" showInWebsite="1" showInStore="1">
            <tab>customtab</tab>
            <label>Section Label</label>
            <resource>MyNamespace_MyModule::mymodule</resource>
            <group id="general" showInDefault="1" showInWebsite="1" showInStore="1" sortOrder="100">
                <label>General</label>
                <field id="custom_config" type="select" showInDefault="1" showInWebsite="1" showInStore="1" sortOrder="100">
                    <label>My Custom Config</label>
                    <source_model>Magento\Config\Model\Config\Source\Yesno</source_model>
                </field>
            </group>
        </section>
    </system>
</config>