[Jetpack Search] Add support for WooCommerce Product Attributes filter

### What

We got a request from a user who wanted to be able to filter the product search results by attribute

### Why

For discoverability of product variations

### How

I'm not sure if this is technically possible due to the way WooCommerce works and that each product can have its own set of attributes. But here's a screenshot with annotations:


The issue names no files, tests, or entry points. Start by locating the Jetpack Search WooCommerce integration and researching how product attributes are indexed and exposed for filtering; done means confirming feasibility and implementing a defined attribute-filter experience for product search results.

Written by the indexing model from the issue text.