Fix `apt-key` deprecated message

[milad-zanganeh]

Pull Request (PR) description

In the current implementation, apt::source stores GPG keys in the trusted.gpg file, which is no longer recommended. Additionally, with the deprecation of apt-key, running the apt update command triggers warnings on Debian-based distributions. This PR modifies the handling of GPG keys so that they are stored in the keyrings directory, aligning with best practices and avoiding the deprecation warnings associated with apt-key

[TheMeier]

given the "new" version for the dependency, should this be marked backward-incompatible?

[kenyon]

given the "new" version for the dependency, should this be marked backward-incompatible?

I think yes, because users of this module who use it with puppetlabs-apt would need to update their puppetlabs-apt module. Same as how we've done for this kind of change in other modules.