adopt puppetlabs apt module
we currently have two codebases to manage APT repositories and keyrings: some stuff spread around torproject_org::apt and base::aptrepo and the puppetlabs-apt module. the latter was imported in our codebase when the postgresql module was imported, as a dependency. it normally does not conflict with our stuff because it's not enabled.
but as part of #31957 (moved) we have to enable it because it's a dependency of the unattended-upgrades module. since we have to bite that bullet anyways, might as well make the best of it and start using the module proper and remove our tpo-specific code associated with it.
so far the only places i spotted use of that code is in torproject_org::apt and the proliant module, which is only used on listera, which probably deserves to be shutdown itself (#33276 (moved)), so this is not as complex a transition as I thought it would be.
the first phase of the transition is to enable the apt module everywhere, with minimal changes. that is a requirement for the deployment of the unattended-upgrades module. then we convert the existing code to use the apt module to create sources.list files and so on.