fix(dashboard,medusa): Fixes to Customer and Customer Groups domains (#7081)

**What**
- Cleanup of domains
- Adds toasts
- Adds delete customer hook
- Fixes validation of create and update customer endpoints.

packages/admin-next/dashboard/src/lib/client/customers.ts

@@ -1,9 +1,10 @@
 import {
   AdminCustomerListResponse,
   AdminCustomerResponse,
+  DeleteResponse,
 } from "@medusajs/types"
 import { CreateCustomerReq, UpdateCustomerReq } from "../../types/api-payloads"
-import { getRequest, postRequest } from "./common"
+import { deleteRequest, getRequest, postRequest } from "./common"
 
 async function retrieveCustomer(id: string, query?: Record<string, any>) {
   return getRequest<AdminCustomerResponse>(`/admin/customers/${id}`, query)
@@ -21,9 +22,14 @@ async function updateCustomer(id: string, payload: UpdateCustomerReq) {
   return postRequest<AdminCustomerResponse>(`/admin/customers/${id}`, payload)
 }
 
+async function deleteCustomer(id: string) {
+  return deleteRequest<DeleteResponse>(`/admin/customers/${id}`)
+}
+
 export const customers = {
   retrieve: retrieveCustomer,
   list: listCustomers,
   create: createCustomer,
   update: updateCustomer,
+  delete: deleteCustomer,
 }