Add required Powershell Gallery CDN URL(s) to endpoint list

The required URL list only shows 'www.powershellgallery.com' as a required URL to download modules.
However, when needing to download modules, the download actually comes from 'https://cdn.powershellgallery.com'.

Please add this URL to the documentation (https://github.com/Azure/AzureStack-Tools/blob/master/HCI/WestEuropeendpoints/westeurope-hci-endpoints.md)