chore: make apis nullable (#7763)

what:

- makes top level attributes of each object an optional field in the http layer where possible

RESOLVES CORE-2229

packages/medusa/src/api/admin/orders/validators.ts

@@ -54,9 +54,9 @@ const Item = z.object({
 
 export const AdminOrderCreateFulfillment = z.object({
   items: z.array(Item),
-  location_id: z.string().optional(),
+  location_id: z.string().nullish(),
   no_notification: z.boolean().optional(),
-  metadata: z.record(z.unknown()).optional(),
+  metadata: z.record(z.unknown()).nullish(),
 })
 
 export type AdminOrderCreateFulfillmentType = z.infer<
@@ -73,7 +73,7 @@ export const AdminOrderCreateShipment = z.object({
   items: z.array(Item),
   labels: z.array(Label).optional(),
   no_notification: z.boolean().optional(),
-  metadata: z.record(z.unknown()).optional(),
+  metadata: z.record(z.unknown()).nullish(),
 })
 
 export type AdminOrderCreateShipmentType = z.infer<