Ubuntu switches to zstd-compressed .debs

Given that there is sufficient archive-wide support for zstd, Ubuntu is switching to zstd compressed packages in Ubuntu 21.10, the current development release. Please welcome hello/2.10-2ubuntu3, the first zstd-compressed Ubuntu package that will be followed by many other built with dpkg (>= 1.20.9ubuntu2), and enjoy the speed!

Sometimes, it's the obscure changes that can have a big impact. This change will speed up the installation of .deb packages.