Switch apt::key from apt-key to trusted.gpg.d

[LirionOSS]

Use Case

From Debian 11 and Ubuntu 22.04 on, apt-key throws a deprecation warning whenever being used, as apt-key stores keys in /etc/apt/trusted.gpg altogether. The new paradigm tells us to use separate files in /etc/apt/trusted.gpg.d/*.gpg.
Also, apt update on Ubuntu 22.04 also now throws warnings whenever somebody or something, e.g. our apt::key, continues to manage apt keys in that very file.

Describe the Solution You Would Like

Change apt::key to populate files in /etc/apt/trusted.gpg.d (e.g. <title>.gpg), which should be treated as keyrings with one or multiple keys inside.

Describe Alternatives You've Considered

Continuing the module as is so far as long as we only get deprecation warnings.

[kenyon]

I think this is a duplicate of #1034.

[LirionOSS]

Duplicate is correct. Feature request can be closed.