Add azurelinux 3.0 images

[sbomer]

Add Azure Linux 3.0 preview images, with the same rootfs setup as the current cbl-mariner-2.0 images, using Ubuntu 16.04. We plan to introduce Ubuntu 18.04 rootfs for .NET 9 builds, so the naming scheme includes the rootfs ubuntu version (for example: azurelinux-3.0-cross-amd64-ubuntu-16.04).

This uses a naming scheme with a -net8.0 suffix. We plan to introduce .NET 9 images with a -net9.0 suffix, that use LLVM 18 and an Ubuntu 16.04 rootfs (if we can find a way to build LLVM 18 there), since we're still aiming to target 16.04 in .NET 9 per #995 (comment):

So image names will look like the following:

• azurelinux-3.0-cross-amd64-net8.0
• azurelinux-3.0-cross-amd64-net9.0

[richlander]

We plan to introduce Ubuntu 18.04

We should hold off on that one. That was the original thinking. I think we've concluded that we'll stay the course on 16.04 for at least another release, if not two. We got feedback that made us pause on this one.

@jkotas

[mthalman]

@lbussell - Be aware of the new pipelines in this PR that will need to be wired up.

[lbussell]

@lbussell - Be aware of the new pipelines in this PR that will need to be wired up.

@mthalman, it seems like the PR validation did run on this PR, so we should merge this and then set up the public and internal pipelines afterwards, right? So that the file is present to create the pipeline against.

[mthalman]

@lbussell - Be aware of the new pipelines in this PR that will need to be wired up.

@mthalman, it seems like the PR validation did run on this PR, so we should merge this and then set up the public and internal pipelines afterwards, right? So that the file is present to create the pipeline against.

Yep, exactly