Use `chromeos` label for chromeos.kernelci.org

The `deploy.py` script can pull together PRs for a particular target branch, such as `main` for `staging.kernelci.org` and `chromeos` for `chromeos.kernelci.org`. It would be good to add an option to also pull PRs that have some particular label(s), for example to have a single PR deployed both on staging and chromeos instances. That way, the code would be directly available on both and there won't be a need to first have it merged on `chromeos` and then port it to `main` or first merge it on `main` and then rebase `chromeos`.