Add support for Alpine 3.21

[ashnaga]

This issue is created to track progress for the work to enable Alpine 3.21 support for .NET 8.0 and 9.0

• [All Product Teams] Compatibility check and infra update
• Do a compatibility check for the product with the new OS
• Replace docker tags used in builds across repos and branches
• Update CI legs to latest updated Dockerfile
• Ensure that the correct Docker images used by teams are built in the dotnet-buildtools-prereqs (if applicable)

[ilyas1974]

Created dotnet/dnceng#4348 to track this work

[mthalman]

Alpine 3.21 is officially released: https://alpinelinux.org/posts/Alpine-3.21.0-released.html