Initial import of the opensmtpd-filters meta-package.

This package provides all the available filter integrations for the
OpenSMTPD mail transfer agent. Included filters are:

* filter-dkimsign
* filter-dnsbl
* filter-rspamd
* filter-senderscore

This package does not contain anything by itself -- it is a
"meta-package" that depends on other packages.  Its sole purpose is
to require dependencies so users can install this package only and
have all the other packages pulled in by the package dependency
mechanism.

(vins)