dovecot: support new `sieve` API in nixpkgs
Since https://github.com/NixOS/nixpkgs/pull/275031 things have became more structured when it comes to the sieve plugin.
Relies on https://github.com/NixOS/nixpkgs/pull/281001 for full features.
Since https://github.com/NixOS/nixpkgs/pull/275031 things have became more structured when it comes to the sieve plugin.
Relies on https://github.com/NixOS/nixpkgs/pull/281001 for full features.