Implement E2E test where we build an example image which is using downstream packages using RH subscription

[odockal]

going through the README of the extension, successful authentication of the user into RH SSO also enabled podman machine to get subscription. And so the images can now be built that can pull downstream packages, ie kernel.

Once signed in, there is nothing further to be done. Podman Desktop will automatically use the SSO token to log into the Red Hat container registry and to register the Linux virtual machine (i.e., podman machine) via subscription-manager.
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To verify that the sign-in process was successful, you may build the following Dockerfile:

FROM registry.redhat.io/rhel9/toolbox
RUN  dnf install -y kernel

Pulling the container image registry.redhat.io/rhel9/toolbox requires having logged into the Red Hat container registry. Installing the kernel package requires access to protected content.

Once signed in, you can now see being logged into the Red Hat Container Registry registry.redhat.io in the Registries menu: