Add apt::keyring defined type

[jps-help]

Summary

Add a new defined type for adding GPG keyrings.

Additional Context

apt-key is deprecated in the latest Debian and Ubuntu releases. Therefore we should move away from the old apt::key defined type which relies on it. With this we can manage apt keyrings directly with the apt module. Further work would be required to integrate this directly into the apt::source like how apt::key is currently. Reference - https://wiki.debian.org/DebianRepository/UseThirdParty

Related Issues (if any)

1034

Checklist

• [x] 🟢 Spec tests - I don't have much experience with this, so I've simply generated the bare-minumum one with pdk.
• [ ] 🟢 Acceptance tests.
• [x] Manually verified. (For example puppet apply)

[CLAassistant]

All committers have signed the CLA.

[kenyon]

Should be closed, was done in #1128.

[smortex]

Thanks @kenyon!