Base class for the server implementation of the service ProductSearch.
Manages Products and ProductSets of reference images for use in product
search. It uses the following resource model:
The API has a collection of ProductSet resources, named
projects/*/locations/*/productSets/*, which acts as a way to put different
products into groups to limit identification.
In parallel,
The API has a collection of Product resources, named
projects/*/locations/*/products/*
Each Product has a collection of ReferenceImage resources, named
projects/*/locations/*/products/*/referenceImages/*