shell: add pixz so NAR serving works from foreman

Dependencies

• [2] 3JXCTKEC Add markdown files for documentation
• [3] WFJGOVMJ Merge branch 'master' of github.com:NixOS/hydra into master
• [4] 7HFOCQ2H Remove nix from hydra-perl-deps
• [5] RWNXH3H2 lastModified -> lastModifiedDate
• [6] 75BCCX2T Get rid of dependency to SQLite

Change contents

• replacement in flake.nix at line 502
  [3.93]→[2.41771:41816](∅→∅)
  − final.nix perlDeps perl mdbook
  [3.93]

  [3.3297]
  + final.nix perlDeps perl mdbook pixz