Update docs to download models from RH registry

[szaher]

Description

Update RHELAI docs to enable model downloading from OCI registries

How to use it

To download ilab models from OCI registries following the following instructions

Note

skopeo must be installed and policy.json file present in $HOME/.config/containers/policy.json or /etc/containers/policy.json
If you don't have skopeo policy, you can download default policy from here

$ ilab model download --repository docker://registry.redhat.io/rhelai1/granite-7b-starter --release 1.2-1728663941
$ cp -r <path-to-model-downloaded-dir>/granite-7b-starter/* s3-data/model

How Has This Been Tested?

Merge criteria:

• The commits are squashed in a cohesive manner and have meaningful messages.
• Testing instructions have been added in the PR body (for PRs involving changes that are not immediately obvious).
• The developer has manually tested the changes and verified that the changes work

[HumairAK]

/lgtm
/approve