Centralize and document GitHub runner images

[ScottTodd]

Our new Linux builder cluster (on Azure) is using https://github.com/saienduri/docker-images/blob/main/ghascale.Dockerfile and we are bringing up a Windows builder cluster using https://github.com/saienduri/arc-windows-runner/blob/main/Dockerfile or https://github.com/Eliasj42/arc-windows-runner/blob/main/Dockerfile. Both of these can be moved into this repository to make it easier for contributors to work with them.

I think we aren't actually using https://github.com/iree-org/base-docker-images/tree/main/docker-github-actions-runner or the _ghr variants of existing dockerfiles (e.g. https://github.com/iree-org/base-docker-images/blob/main/dockerfiles/cpubuilder_ubuntu_jammy_ghr.Dockerfile). As part of moving those dockerfiles to this repo, we can either remove the _ghr variants entirely or fold those Dockerfiles into the existing ones and switch the runner clusters to use them. If we fold the Dockerfiles in, we may be able to drop the Docker-in-Docker setup in our workflow files:

    container:
      image: ghcr.io/iree-org/cpubuilder_ubuntu_jammy@sha256:78a558b999b230f7e1da376639e14b44f095f30f1777d6a272ba48c0bbdd4ccb

For the Windows Dockerfile, we should add docs like what I have drafted at https://gist.github.com/ScottTodd/4c6126702b14ff3275e1553be451c7f4. Note that Windows does not support Docker-in-Docker while Linux does.