This simplifies the setup to receive emails from the ZFS Event Daemon
by relying on the sendmail wrapper defined by other modules such as
msmtp or Postfix.
This is more similar to how other modules like smartd deal with email
configuration.
The user is no longer required to define and rebuild their own ZFS
package to add email support.
GitHub: closes https://github.com/NixOS/nixpkgs/issues/132464
cf6d89525f