Migrate dotnetbuilds CDN from edgeio to Azure FD

[mmitche]

We need to migrate dotnetbuilds over to AzureFD due to the Edgio CDN going away. Unlike dotnetcli, we can change the hostname in the places it is referenced (dotnetbuilds.azureedge.net). dotnetbuilds is not intended for general public consumption of .NET bits, though it is referenced in our official install scripts.

Execution Steps

The plan for migration off of dotnetbuilds is as follows:

1. Create a new CDN that points to the dotnetbuilds storage account. This CDN will have the same settings as the previous CDN. Note that azurefd FQDNs include a hash and are less friendly to work with.
2. Determine and create a short form URL that should point to the new dotnetbuilds CDN. This short form could be a subdomain of dot.net, or an aka.ms link, etc.
3. Generate an announcement and corresponding issue on https://github.com/dotnet/core/discussions detailing the following:

• Old name that is going away
• Timeline that it may go away (sometime after 15th Jan)
• New URI to update to.

4. Update all referenced locations that point to the existing CDN URI. This includes:

• Existing aka.ms links
• SDK daily builds table
• aka.ms link targets in publishing (I think?)
• Some yaml files that specify download locations for dotnet-install
• eng/common scripting across all in support .NET versions
• install-dotnet.ps1
• ...

When the old URI dies, the announcement should be updated to indicate that this is the case.

[mmitche]

@dotnet/dnceng

[lbussell]

.NET Dockerfiles reference dotnetbuilds for nightly builds and some other releases. Today only the Aspire Dashboard Dockerfile references it. We would add more references when we add .NET 10 nightly Dockerfiles, but obviously we will just point that at wherever the new build location is. We can update these at any time, but historical nightly Dockerfiles will fail to build.

/cc @mthalman @joperezr

[mthalman]

This also affects WinGet packages: https://github.com/microsoft/winget-pkgs/blob/09f04f8a043740386e3db3ae7f71cad5277b59ea/manifests/m/Microsoft/DotNet/SDK/9/9.0.101/Microsoft.DotNet.SDK.9.installer.yaml#L14

Sorry, this issue is for dotnetbuilds, which WinGet packages is not referencing.