Replace usage of `apt_key` in ansible tasks

[mboersma]

Is your feature request related to a problem? Please describe.

Image builder is using the Ansible apt_key module, but it is deprecated as specified in the module notes. It may stop working with Ubuntu 24.04.

Describe the solution you'd like

A more future-proof way is using the get_url module as described in this blog post, for example.

I tried that approach in #1280 but could not get it to work on Ubuntu 20.04, only 22.04, so I stuck with the working apt_key approach for now.

Describe alternatives you've considered

Additional context

/kind feature