After having created the agent ISO, the agent-nmtui must be added to the ISO using the following approach:
1. Unpack the agent ISO in a temporary folder
2. Unpack the /images/ignition.img compressed cpio archive in a temporary folder
3. Create a new ignition.img compressed cpio archive by appending the agent-nmtui
2. Create a new agent ISO with the updated ignition.img

Implementation note
Portions of code from a PoC located at https://github.com/andfasano/gasoline could be re-used