Set custom product attributes

There seems to be no documentation on how to set custom product attributes through entity data. I searched through the example tests and tried a few things to no avail.

Preconditions

1. MFTF v3

Steps to reproduce

1. Create custom attribute entity

    <entity name="SubscriptionIsEnabled" type="custom_attribute">
        <data key="attribute_code">sub_enabled</data>
        <data key="value">1</data>
    </entity>

2. Create a product entity

    <entity name="SubscriptionProduct" extends="SimpleProduct">
        <data key="name">Simple Subscription</data>
        <data key="sku" unique="suffix">simple-trial-2</data>
        <data key="urlKey" unique="suffix">simple-trial-2</data>
        <requiredEntity type="custom_attribute">SubscriptionIsEnabled</requiredEntity>
    </entity>

3. Create the product in a <before> block of a Suite

    <createData entity="SubscriptionProduct" stepKey="createSubscriptionProduct">
        <requiredEntity createDataKey="createCategory"/>
    </createData>

Expected result

1. The product's sub_enabled custom attribute should be set

Actual result

1. The attribute is not set

Start with the MFTF v3 entity examples and tests for custom_attribute entities, then trace how the createData step in a Suite before block applies product data. Document the working syntax for setting a product custom attribute through entity data, including the requiredEntity relationship, and verify that the sub_enabled attribute is set on the created product.