nixos/dovecot: update for 2.4

Author: Jappie3

nixos/doc/manual/release-notes/rl-2605.section.md

@@ -63,6 +63,8 @@ of pulling the upstream container image from Docker Hub. If you want the old beh
 
 <!-- To avoid merge conflicts, consider adding your item at an arbitrary place in the list instead. -->
 
+- `services.dovecot` now supports the Dovecot 2.4 configuration format while maintaining compatibility with Dovecot 2.3.
+
 - `services.frp` now supports multiple instances through `services.frp.instances` to make it possible to run multiple frp clients or servers at the same time.
 
 - `services.openssh` now supports generating host SSH keys by setting `services.openssh.generateHostKeys = true` while leaving `services.openssh.enable` disabled.  This is particularly useful for systems that have no need of an SSH daemon but want SSH host keys for other purposes such as using agenix or sops-nix.