The image builds are trying to fetch a gpg pubkey from keybase which
does not exist. This causes the builds to fail. Fix this by vendoring
the key in the swift repo directly. This should be more reliable.
Upstream bug at https://github.com/just-containers/s6-overlay/issues/352
Note I looked up the pubkey given the hash on that issue and copied its
contents into this change. I can't vouch for the validity of this key
beyond that. However, if it is listed in that issue and validates the
packages from s6 then it is probably good.
Change-Id: I3f42fbaae5f246836024f95b549b487b41bd6f1d
930ac1114b