…iptions

Motivation for this change

Several service definitions used mkEnableOption with text starting with "Whether to", which produced funny option descriptions like "Whether to enable Whether to run the rspamd daemon..".

This commit corrects this, and adds short descriptions of services to affected service definitions.

I didn't test this change at all, but since it's trivial one-line documentation changes, I figured this won't be required.

Things done

• 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.