Add non-packager (support staff) keys

As discussed in wkd#2 (closed) it would be good to also add our support staff keys to the keyring structure (e.g. in a staff directory).

Our support staff members need to be able to receive encrypted mails and sign software releases, but they are not part of the package maintainers (unless a member has both roles). As such the keyringctl build command should exclude their keys from the archlinux.gpg file, but they should be made available to WKD exports.