Add parent ids to Product extension attributes

[smoucka]

Description

This PR adds an extension attribute to the Products API data interface, both individual and bulk requests.

This uses the built-in Configurable resource's method getParentIdsByChild. Will return an empty array if the product is not associated with a parent.

Manual Testing Steps

1. Update extension and make request to /index.php/rest/V1/products or /index.php/rest/V1/products/:sku route.
2. Example response:

    "extension_attributes": {
        "website_ids": [
            1
        ],
        "category_links": [
            ...
        ],
        "stock_item": {
            ...
        },
        "kl_parent_ids": [
            2
        ]
    }

Pre-Submission Checklist:

• You've updated the CHANGELOG following the steps here
• Internal Only - If this is a release, please confirm the following:
  • The links in the changelog have been updated to point towards the new versions
  • The version has been incremented in the following places: module.xml and composer.json

NOTE: Please use the Changelogger cli tool to manage versioned file upgrades.

[kamidzi-klaviyo-integrations]

maybe a test?