add is_disabled to create sales channel (#1928)

**What**
- include `is_disabled` when creating a sales channel

**Why**
- To enable creation of draft sales channels

packages/medusa/src/api/routes/admin/sales-channels/create-sales-channel.ts

@@ -1,5 +1,5 @@
 import { Request, Response } from "express"
-import { IsOptional, IsString } from "class-validator"
+import { IsBoolean, IsOptional, IsString } from "class-validator"
 
 import SalesChannelService from "../../../../services/sales-channel"
 import { CreateSalesChannelInput } from "../../../../types/sales-channels"
@@ -44,4 +44,8 @@ export class AdminPostSalesChannelsReq {
   @IsString()
   @IsOptional()
   description: string
+
+  @IsBoolean()
+  @IsOptional()
+  is_disabled?: boolean
 }