RHOAIENG-21668: chore(gha): mount Red Hat subscription in GitHub Actions

Here's how this is supposed to work.

On a subscribed machine, podman mounts the secrets directory into the container as a volume.

```
$ cat /usr/share/containers/mounts.conf
/usr/share/rhel/secrets:/run/secrets
```

Furthermore, there may be ``/run/secrets/etc-pki-entitlement` and ``/run/secrets/rhsm`.

The approach that actually worked for me is https://access.redhat.com/solutions/5558771

First, `subscription-manager` detects a container and behaves differently there.
So, run `subscription-manager` with `SMDEV_CONTAINER_OFF=1` to subscribe container as if it was a physical machine.

Then, look into `/etc/pki/entitlement` for certificates as suggested in https://grep.be/blog//en/work/The_future_of_the_eID_on_RHEL/

```
podman run --platform=linux/amd64 -v/Users/jdanek/IdeaProjects/notebooks/ci/secrets/run/secrets:/mnt  --rm -it registry.access.redhat.com/ubi9/ubi

    1  subscription-manager register --username
    3  cp -R /etc/pki/entitlement /mnt/etc-pki-entitlement
    5  cp -R /etc/rhsm /mnt/rhsm
    7  cp /etc/yum.repos.d/redhat.repo /mnt/redhat.repo
```

Finally, copy out and store the certificates as CI secrets for reuse in jobs.

Author: jiridanek

ci/cached-builds/mounts.conf

@@ -0,0 +1,5 @@
+# /usr/share/containers/mounts.conf
+# https://github.com/containers/common/issues/1735
+
+/etc/pki/consumer:/etc/pki/consumer
+/etc/pki/entitlement:/etc/pki/entitlement