Breaking changes for all users of `varnish`, which is renamed to `vinyl-cache`

The Varnish project has .
This upgrade results in breaking changes and users are advised to study these changes and how it affects them before following the replacement.
All references to "varnish" have been changed to "vinyl" in all binaries and directories.

At minimum, users will have to:

• rename /etc/varnish to /etc/vinyl-cache


• rename /var/lib/varnish to /var/lib/vinyl-cache


• fix up ownership of files inside /var/lib/varnish


• user varnish becomes vinyl


• group varnish becomes vinyl


• user varnishlog becomes vinyllog


• user vcache remains the same


• disable the old varnish.service and varnishncsa.service systemd units


• enable the new vinyl-cache.service and vinylncsa.service systemd units

Meanwhile, the varnish package has been dropped from [extra].
We're not currently planning to maintain a new varnish package as it's a different upstream project.