By default rspamd will look for multiple files in /etc/rspamd/local.d
and /etc/rspamd/override.d to be included in subsections of the merged
final config for rspamd. Most of the config snippets in the official
rspamd documentation are made to these files and so it makes sense for
NixOS to support them and this is what this commit does.
As part of rspamd 1.8.1 support was added for having custom Lua
rules stored in $LOCAL_CONFDIR/rspamd.local.lua which means that it is
now possible for NixOS to support such rules and so this commit also
adds support for this to the rspamd module.
The socket activation I added to the rspamd module doesn't actually work
and can't be made to work without changes to rspamd.
See: #47421
See: rspamd/rspamd#2035
