feat(flake.nix): switch dogfood dev image to buildNixShellImage from dockerTools#16223

ThomasK33 merged 2 commits intomaincoder/coder:mainfrom

01-22-feat_flake.nix_switch_dogfood_dev_image_to_buildnixshellimage_from_dockertoolscoder/coder:01-22-feat_flake.nix_switch_dogfood_dev_image_to_buildnixshellimage_from_dockertoolsCopy head branch name to clipboard