Add GnuPG to Omnibus for improved GPG key support
Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/36845
We need to package GnuPG and possibly GPGME as part of omnibus to support Ed25519 keys.
cc @marin @DouweM this came from https://gitlab.com/gitlab-org/gitlab-ce/issues/36845#note_39249673