feat(medusa) allow querying category descendants with a param in list endpoint (#3321)

What:

Allowing the list endpoint to return a full tree when requested. 

Why:

When scoped with parent_category_id=null and include_descendant_tree=true, the query cost is fairly low. This allows for fast querying and prevent FE from building out the entire tree from a flat list repeatedly. By default, it is set to false, so this should be an intentional change knowing the costs of doing it for the entire result set. 

How:

When include_descendants_tree is included in the request parameter or the service parameter, we do a loop on results of product categories and do a call to fetch the descendants of that product category. 

RESOLVES CORE-1128

packages/medusa/src/api/routes/admin/product-categories/list-product-categories.ts

@@ -15,6 +15,7 @@ import { extendedFindParamsMixin } from "../../../../types/common"
  *   - (query) q {string} Query used for searching product category names orhandles.
  *   - (query) is_internal {boolean} Search for only internal categories.
  *   - (query) is_active {boolean} Search for only active categories
+ *   - (query) include_descendants_tree {boolean} Include all nested descendants of category
  *   - (query) parent_category_id {string} Returns categories scoped by parent
  *   - (query) offset=0 {integer} How many product categories to skip in the result.
  *   - (query) limit=100 {integer} Limit the number of product categories returned.
@@ -92,6 +93,10 @@ export class AdminGetProductCategoriesParams extends extendedFindParamsMixin({
   @IsOptional()
   q?: string
 
+  @IsString()
+  @IsOptional()
+  include_descendants_tree?: boolean
+
   @IsString()
   @IsOptional()
   is_internal?: boolean