In nixpkgs we expose `services.dovecot.hasNewUnitName` option that can be
safely inspected to understand that whether to use the `dovecot` systemd
service name instead of `dovecot2`.
Enabling the rspamd debug log drowns out everything else and should be
selected explicitly as needed.
The external test does not require it and removing it makes it much
(~40.5%) faster, since it now does not block on terminal output anymore.
Before:
```
Benchmark 1: nix build .#hydraJobs.x86_64-linux.external-unstable --rebuild
Time (mean ± σ): 151.737 s ± 1.074 s [User: 0.310 s, System: 0.289 s]
Range (min … max): 150.321 s … 153.512 s 10 runs
```
After:
```
Benchmark 1: nix build .#hydraJobs.x86_64-linux.external-unstable --rebuild
Time (mean ± σ): 90.531 s ± 0.557 s [User: 0.054 s, System: 0.045 s]
Range (min … max): 89.579 s … 91.278 s 10 runs
```
This switches the full-text search plugin from fts-xapian to
fts-flatcurve, the now preferred indexer still powered by Xapian,
which will be integrated into Dovecot core 2.4.
This sets a sane minimal configuration for the plugin with
international language support.
The plugin options marked as "advanced" in Dovecot's documentation
aren't re-exposed for simplicity. They can nevertheless be overridden
by module consumers by directly setting keys with
`services.dovecot2.pluginSettings.fts_*`.
The `fullTextSearch.maintenance` option is removed as the index is now
incrementally optimised in the background.
GitLab: closes https://gitlab.com/simple-nixos-mailserver/nixos-mailserver/-/issues/239
fts xapian does not publish configuration changes in a changelog. As a
result, some options that nixos mailserver was setting for it have been
ignored for several years. New options (process_limit) are now
recommended. This adapts the module to these changes.
The default value of partial= is 2, but fts_xapian 1.8.3 now requires it
to be at least 3, and fails loudly in case it is 2. As a result, this
change is required to support fts_xapian 1.8.3 and later.
