Extract agent-tui from agent-installer-utils when creating the agent ISO

Currently the `agent create image` command takes care to extract the agent-tui binary (and required libs) from the `assisted-installer-agent` image (shipped in the release as `agent-installer-node-agent`).
Once the agent-tui will be available instead from the `agent-installer-utils` image, it would be necessary to update accordingly the installer code (see https://github.com/openshift/installer/blob/56e85bee78490c18aaf33994e073cbc16181f66d/pkg/asset/agent/image/agentimage.go#L81)