Validating that we need the CI and PR containers

[richlander]

I was looking at the various pipelines for this repo. From the perspective on main, they are all stale. We should / need to remediate all of them. Before we do that, it would good to understand why they are needed. My goal is that main is pristine before it enters servicing.

sdk/.vsts-pr.yml

Lines 29 to 39 in a1da6b6

	containers:
	- container: alpine319WithNode
	image: mcr.microsoft.com/dotnet-buildtools/prereqs:alpine-3.19-WithNode
	- container: centosStream9
	image: mcr.microsoft.com/dotnet-buildtools/prereqs:centos-stream9
	- container: debian12Amd64
	image: mcr.microsoft.com/dotnet-buildtools/prereqs:debian-12-gcc14-amd64
	- container: fedora39
	image: mcr.microsoft.com/dotnet-buildtools/prereqs:fedora-39
	- container: ubuntu2204DebPkg
	image: mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-22.04-debpkg

sdk/.vsts-ci.yml

Lines 66 to 76 in a1da6b6

	containers:
	alpine319WithNode:
	image: mcr.microsoft.com/dotnet-buildtools/prereqs:alpine-3.19-WithNode
	centosStream9:
	image: mcr.microsoft.com/dotnet-buildtools/prereqs:centos-stream9
	debian12Amd64:
	image: mcr.microsoft.com/dotnet-buildtools/prereqs:debian-12-gcc14-amd64
	fedora39:
	image: mcr.microsoft.com/dotnet-buildtools/prereqs:fedora-39
	mariner20CrossArm:
	image: mcr.microsoft.com/dotnet-buildtools/prereqs:cbl-mariner-2.0-cross-arm

[richlander]

@marcpopMSFT @sbomer @jkoritzinsky @mthalman @baronfel

[marcpopMSFT]

These were copied over from the installer repo. We use all 5 in our PR pipeline and used to run the installer tests on them. They didn't work for the SDK tests so we disabled all tests in these legs for now but should bring back a subset of the tests. Maybe just the End2End.

For CI, we use alpine, centos, and mariner for building the various tars we ship.

I would have to defer to the A&D team over which of these are important to keep in the PR pipeline and how to upgrade them.

[richlander]

@MichaelSimons @mthalman