Update versions to address VSV00008 vulnerability

[samford]

This updates to the 6.0.10, 6.6.2, and 7.0.2 versions of Varnish (released 2022-01-25), addressing the VSV00008 HTTP/1 Request Smuggling Vulnerability. More information here: https://varnish-cache.org/security/VSV00008.html

A couple other things to note:

• This PR also updates the varnish-cache.org tarball URLs in template files to use HTTPS instead of HTTP. If there's a technical reason behind using HTTP, just let me know and I'll drop the commit, re-run populate.sh, and update this branch.
• Similarly, this updates varnish-cache.org tarball URLs in template files to use the /downloads/ path (e.g., https://varnish-cache.org/downloads/varnish-7.0.2.tgz), as currently used on the Varnish website (e.g., the tarball link on the 7.0.2 release page). varnish-cache.org previously used URLs with a /_downloads/ path (e.g., https://varnish-cache.org/_downloads/varnish-7.0.2.tgz) but this changed to /downloads/ sometime in the past couple months. The /_downloads/ URLs continue to resolve (200) but this could break in the future, so it's probably best to update these URLs to align with the links on varnish-cache.org.

[gquintard]

thank you @samford , merged! If you feel like it, you can also open a PR to https://github.com/docker-library/official-images and I'll back you up. Otherwise, I'll open it tonight.

In any case, thanks a bunch!