[site-reviews] auto create/assign CPT category for reviews

/**
 * This snippet assumes that you have two CPT: Restaurant and Food,
 * and that you have somehow connected these two post objects (i.e. A Restaurant has many Foods).
 *
 * Since Site Reviews v4 does not allow you to assign reviews to multiple Post IDs,
 * the solution is to assign reviews to the Food CPT ID, and then have Site Reviews
 * automatically assign the reviews to a restaurant category with slug that contains
 * the Restaurant CPT Post ID. If the restaurant category does not exist, it will be
 * created when a review is submitted. This category can then be used to target all
 * food reviews for the restaurant.
 *
 * Please pay attention to the @todo in the snippet below
 *
 * If you need to manually create the restaurant categories for existing reviews,
 * the category slug must look like this: "restaurant_123" where "123" is the
 * Restaurant Post ID.
 *
 * @param \GeminiLabs\SiteReviews\Review $review
 * @return void
 */
add_action('site-reviews/review/created', function ($review) {
    $assignedToIds = array_filter((array) $review->assigned_to);
    foreach ($assignedToIds as $foodPostId) {

        // @todo you need edit this part to get the associated restaurant post from the food post ID
        $restaurantPostId = '';

        $restaurant = get_post($restaurantPostId);
        if (empty($restaurant->ID)) {
            continue;
        }
        $termSlug = 'restaurant_'.$restaurant->ID;
        if (!term_exists($termSlug, glsr()->taxonomy)) {
            wp_insert_term($restaurant->post_title, glsr()->taxonomy, ['slug' => $termSlug]);
        }
        wp_set_object_terms($review->ID, $termSlug, glsr()->taxonomy);
    }
});