fix(medusa): validate customer for group discount (#3797)

* fix: validate customer for group discount

* fix: remove logger

* fix: add generated desc

* fix: add an integration test case

* refactor: update error message

* fix: typo

* refactor: move condition

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Co-authored-by: fPolic <frane@medusajs.com>

packages/medusa/src/api/routes/store/carts/update-cart.ts

@@ -168,7 +168,7 @@ class Discount {
  *         - code
  *       properties:
  *         code:
- *           description: "The code that a Discount is identifed by."
+ *           description: "The code that a Discount is identified by."
  *           type: string
  *   customer_id:
  *     description: "The ID of the Customer to associate the Cart with."