docs: added Manage Customers documentation (#2911)

* docs: added Manage Customers documentation

* fixed link

docs/content/advanced/backend/customers/index.md

@@ -74,4 +74,5 @@ The relation between the `Customer` and `Address` entities is available on both
 ## See Also
 
 - [Implement customer profiles in the storefront](../../storefront/customer-profiles.mdx)
+- [Manage customers using the admin APIs](../../admin/manage-customers.mdx)
 - Customers [Admin](/api/admin/#tag/Customer) and [Storefront](/api/store/#tag/Customer) API References

docs/content/advanced/backend/sales-channels/manage-admin.mdx

@@ -1,7 +1,7 @@
 import Tabs from '@theme/Tabs';
 import TabItem from '@theme/TabItem';
 
-# How to Use SalesChannels APIs
+# How to Manage Sales Channels
 
 In this document, you’ll learn how to manage sales channels and their products and orders using the Admin APIs.