added Azure Stack HCI 23H2 CU and Servicing Stack 
in a new PR we should remove SSU as they are now part of the CU for all supported releases of Windows Server and Client AFTER 1607

ref: https://www.catalog.update.microsoft.com/Search.aspx?q=servicing%20stack

1. added support for Windows Server 11 23H2
2. added support for Azure Stack HCI 23H2
3. removed "," in Searchstring for consistency, -like is used later on
4. changed SSUSearchString to $null where appropriate (no SSU exist for these releases. left it for older ones, even though latest CUs would have them included.
5. added if else to support $null SSUSearchString

notes: for some reason 23H2 releases do not download files even they are correctly found and listed. Problem with the used module Get-MSCatalogUpdate?

Update DownloadLatestCUs.ps1 - support 23H2 releases and empty SSUString where no longer needed

Update DownloadLatestCUs.ps1