A self hostable nixpkgs review bot

Things warden already does:

• [ ] Build all packages updated/added in a pr (by parsing commits)
• [ ] Run statix and deadnix on all code
• [ ] Run nixpkgs-lint for all packages update/added in a pr (by parsing commits)
• [ ] Summarize the information

Things to do:

• [ ] Make it an actual bot
• [ ] Verify passthru.tests https://github.com/IogaMaster/warden/issues/1
• [ ] Clean up the codebase
• [ ] Allow for reviewing HEAD of the current repo
• [ ] Use the new version of nixpkgs-lint