Creates relations from the source product id to every target product listed in the request body, all under the
relation definition relationId. Use this to add many related products in a single call; to relate to just one
product use POST /products/{id}/connections/products. The operation is all-or-nothing: if the source product,
the relation definition, or any target product does not exist, or if any target is already related to the source
under this relation definition, the call fails and no relations are created.

For more details on working with
products and relations, refer to the Add product relations.