evolution-registry-source is a service in gnome3.evolution-data-server so you will need to add that to systemd.packages. services.gnome3.evolution-data-server.enable = true; will do that for you.
For the dconf warning, you will need programs.dconf.enable = true;.
But the main issue is that evolution-ews was just recently packaged and to be able to use it, we need something like WIP: Evolution with plugins by dasj19 · Pull Request #92775 · NixOS/nixpkgs · GitHub.