Integration between GPG Sync and OpenPGP CA

[hko-s]

As we discussed, we'd like to work on two aspects of interaction between GPG Sync and OpenPGP CA (https://gitlab.com/openpgp-ca/openpgp-ca):

1. We want to implement generation of GPG Sync-style keylists in OpenPGP CA
2. Extending GPG Sync to facilitate/simplify a set of workflows on user machines (generate OpenPGP CA-style signatures, pre-generate revocation certificates, ...)