Public keys scraps will accept a repository index signature from.

Every .pub file here is tried in turn, so a key can be rotated by shipping
the new one beside the old and removing the old once the repositories have
moved over. These are signify keys - Ed25519, one line - and the matching
secret key is not on this machine and is not in any ScrapLinux repository.

A repository decides how much its signature matters, in its .repo file:

    sig = required   an index without a good signature is not used
    sig = optional   checked when it can be, warned about otherwise (default)
    sig = off        not checked

ScrapLinux's own repositories are signed. They are shipped as "optional" while
the installation image is still built without signify on it; set them to
"required" on a machine that has signify installed, which is every machine
that installed the base system.
