Documentation on .NET infrastructure reuse decisions

Currently there are a some bits we aren't reusing from .NET infrastructure:

• https://github.com/dotnet/dotnet-buildtools-prereqs-docker
  • At first glance doesn't seem right to put our prereqs in repo with dotnet in the name.
  • Docker team is hesitant.
  • Short-term, we are using an image produced by this repo. Long-term we plan to not ask to put our own images into this repo, and make our own instead.
• An ACR, or publishing into MCR.
  • Not investigated in detail. Similar factors as dotnet-buildtools-prereqs-docker.
  • ACR: my understanding is the current ACRs are very .NET-specific, and there are already multiple in use for parts of .NET. Even if we reused, we may need to create our own.
  • MCR: I believe this is public and broader than .NET.
• dotnetcli.blob.core.windows.net
  • dotnet.
  • A storage account seems relatively easy to maintain: reuse is not as inherently beneficial as most other items.
  • Haven't discussed with .NET team.
• Maestro++/BAR and associated publishing infra
  • Designed for .NET build orchestration and .NET's artifacts in particular. Not necessarily easy to adapt. (Up-front cost.)
  • We have a simple release scenario compared to .NET: one repo, simple acquisition.
  • Haven't discussed with .NET team.

We are reusing:

• Signing infrastructure.
  • Both Arcade's SignTool and underlying VS Eng MicroBuild.
  • MicroBuild tooling interacts with ESRP on our behalf.
• SDL validation scripts, running Guardian (in progress).
  • Acquiring and running Guardian isn't trivial. This is at least a starting point.
• GitHub -> AzDO mirroring infra, Maestro.
• https://github.com/dotnet/docker-tools (planned)
  • Used to maintain and build a repo with Dockerfiles with bonus features for dependency tracking and templating.

Filing this issue to keep track of which bits are are/aren't reusing and why. (May want to turn this into a checked-in doc at some point.)

The issue names no target file or test. Start by reviewing the listed .NET infrastructure repositories and the reuse decisions in the issue; done would be a checked-in document capturing which components are and are not reused and why, if that scope is confirmed.