Assets job to fallback to workhorse instead of omniubs

What

Currently, the assets job fetches the assets from the assets docker image then uploads it to our gcp bucket, if the image is not available, it falls back to fetching the assets from omnibus. https://ops.gitlab.net/gitlab-com/gl-infra/deploy-tooling/-/blob/master/bin/fetch-and-upload-assets?ref_type=heads#L190-193

    if ! fetch_from_registry; then
        echo "Fetching from registry not available, fetching assets from package instead"
        fetch_from_pkg
    fi

Solution

We need to fallback to using the workhorse image instead of omnibus #19679 (comment 1590138994)

would it make sense to fallback to grabbing it from the auto-deploy CNG workhorse image? It's a little odd to still be using the omnibus package considering the majority of gitlab.com is using the images. And in the case that you can't pull the workhorse image, then that's likely already a blocker to rolling out the latest auto-deploy.

---

Mainly we need to replace this:

https://ops.gitlab.net/gitlab-com/gl-infra/deploy-tooling/-/blob/master/bin/fetch-and-upload-assets?ref_type=heads#L64-84 To fetch it from the image instead.