Associations

sure would be nice if the repositories, when constructing the entities, would hydrate associated data. Similar to [CakePHP](https://book.cakephp.org/4/en/orm/associations.html) or [TypeOrm](https://typeorm.io/relations).

[According to the Rest API Handbook](https://developer.wordpress.org/rest-api/using-the-rest-api/linking-and-embedding/#embedding), some associated data can be fetched in a single call.

Start by reviewing how repositories construct entities and the WordPress REST API linking and embedding guidance referenced in the issue. Define which associated data should be hydrated, how supported associations are requested, and what the completed behavior should be before locating the relevant implementation and tests.

Written by the indexing model from the issue text.