fix(search): add missing default product relations (#4008)

* fix(search): add missing default product relations

Add missing default product relations for events calling SearchService.addDocuments

For the following events: `ProductService.Events.UPDATED,  ProductVariantService.Events.CREATED, ProductVariantService.Events.UPDATED]`,
`SearchService.addDocuments` will fail due to `product` missing its `variants` relations.

The issue can be observed with the Algolia plugin where `reduce` is being attempted on `product.variants`.
https://github.com/medusajs/medusa/blob/develop/packages/medusa-plugin-algolia/src/utils/transformer.ts#L14

Implement the same retrieve pattern as `handleProductCreation` method.

* chore(changeset): patch

---------

Co-authored-by: Oliver Windall Juhl <59018053+olivermrbl@users.noreply.github.com>

.changeset/warm-ways-leave.md

@@ -0,0 +1,5 @@
+---
+"@medusajs/medusa": patch
+---
+
+fix(search): add missing default product relations

packages/medusa/src/subscribers/product.ts

@@ -62,7 +62,9 @@ class ProductSearchSubscriber {
   }
 
   handleProductUpdate = async (data) => {
-    const product = await this.productService_.retrieve(data.id)
+    const product = await this.productService_.retrieve(data.id, {
+      relations: defaultSearchIndexingProductRelations,
+    })
     await this.searchService_.addDocuments(
       ProductService.IndexName,
       [product],
@@ -75,7 +77,9 @@ class ProductSearchSubscriber {
   }
 
   handleProductVariantChange = async (data) => {
-    const product = await this.productService_.retrieve(data.product_id)
+    const product = await this.productService_.retrieve(data.product_id, {
+      relations: defaultSearchIndexingProductRelations,
+    })
     await this.searchService_.addDocuments(
       ProductService.IndexName,
       [product],