fix(medusa): Add to default admin customer fields (#7126)

**What**
- Adds `has_account` to the default fields returned by the API.

**Why**
- The field is used heavily in the admin dashboard, so it makes sense to include it out of the box.

packages/medusa/src/api-v2/admin/customers/query-config.ts

@@ -5,6 +5,7 @@ export const defaultAdminCustomerFields = [
   "last_name",
   "email",
   "phone",
+  "has_account",
   "created_by",
   "created_at",
   "updated_at",