Plumb a signing callback function to `unixpkgs.rpmTarget` to allow
signing RPMs. This callback is optional and RPMs will build unsigned if
not set, just as before.
Updates https://github.com/tailscale/tailscale/issues/1882
Signed-off-by: Andrew Lytvynov <awly@tailscale.com>
Pass an optional PEM-encoded ECDSA key to `cmd/dist` to sign all built
tarballs. The signature is stored next to the tarball with a `.sig`
extension.
Tested this with an `openssl`-generated key pair and verified the
resulting signature.
Updates #8760
Signed-off-by: Andrew Lytvynov <awly@tailscale.com>
