feat(medusa): Prevent default channel from being deleted (#1835)

**What**
Prevent the default channel from being deleted

Fixes CORE-317

integration-tests/api/factories/simple-sales-channel-factory.ts

@@ -1,11 +1,12 @@
-import { Connection } from "typeorm"
-import faker from "faker"
 import { SalesChannel } from "@medusajs/medusa"
+import faker from "faker"
+import { Connection } from "typeorm"
 
 export type SalesChannelFactoryData = {
   name?: string
   description?: string
   is_disabled?: boolean
+  id?: string
 }
 
 export const simpleSalesChannelFactory = async (
@@ -20,7 +21,7 @@ export const simpleSalesChannelFactory = async (
   const manager = connection.manager
 
   const salesChannel = manager.create(SalesChannel, {
-    id: `simple-id-${Math.random() * 1000}`,
+    id: data.id ?? `simple-id-${Math.random() * 1000}`,
     name: data.name || faker.name.firstName(),
     description: data.description || faker.name.lastName(),
     is_disabled: