Identify suitable off-machine location for storing private build container images

[sxa]

Due to licensing issues we cannot ship the RHEL/s390x build image to the public so it will need to be in a private location. This issue covers identifying somewhere suitable.

Follow-up to #2731

Noting also that at present the images are not being automatically regenerated when the playbooks are updated, which could be a first step that can be done before pushing it externally.

[sxa]

Related: #3182

[sxa]

This is also relevant for the newly tested docker images for Windows which will also need to be in a private repository so they can be shared:

Options:

• Dockerhub private registry (Subject to any licensing restrictions on those repositories)
• Azure Container Registry (Potentially best suited for our Windows Azure hosts
• GitHub container registry (ghcr.io)
• quay.io
• Self-hosted?
• Something else?

Noting that the OpenJ9 team use a private repository so that is known to work well.

[sxa]

@gdams Since you're more likely to be familiar with it (and I understand from earlier discussions this might be outside our sponsored credits) can you look at what we need to get us set up with ACR for Windows (and probably s390x for now) build docker images?

[gdams]

I had an old container registry setup a while ago (adoptium.azurecr.io). There's a few steps to getting it running in a GH actions env