Motivation for this change

Redmine was marked as broken and abandoned.

Things done

• updated the redmine package
• migrated to the new ruby infrastructure (see issue Migrate redmine to the new ruby infrastructure #5984)
• reworked the service and added a database.passwordFile option
• briefly tested with mysql as a database, though not postgresql

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Fits CONTRIBUTING.md.

This should also solve issue #11560