feature: provide better rspamd suppport (#3016)

* added options to toggle OpenDKIM & OpenDMARC

rspamd can provide DKIM signing and DMARC checking itself, so users
should be able to disable OpenDKIM & OpenDMARC. The default is left at
1, so users have to to opt-in when the want to disable the features.

* misc small enhancements

* adjusted start of rspamd

The order of starting redis + rspamd was reversed (now correct) and
rspamd now starts with the correct user.

* adjusted rspamd core configuration

The main configuration was revised. This includes AV configuration as
well as worker/proxy/controller configuration used to control the main
rspamd processes.

The configuration is not tested extensively, but well enough that I am
confident to go forward with it until we declare rspamd support as
stable.

* update & improve the documentation

* add tests

These are some initial tests which test the most basic functionality.

* tests(refactor): Improve consistency and documentation for test helpers (#3012)

* added `ALWAYS_RUN` target `Makefile` recipies (#3013)

This ensures the recipies are always run.

Co-authored-by: georglauterbach <44545919+georglauterbach@users.noreply.github.com>

* adjusted rspamd test to refactored test helper functions

* improve documentation

* apply suggestions from code review (no. 1 by @polarthene)

Co-authored-by: Brennan Kinney <5098581+polarathene@users.noreply.github.com>

* streamline heredoc (EOM -> EOF)

* adjust rspamd test (remove unnecessary run arguments)

Co-authored-by: Brennan Kinney <5098581+polarathene@users.noreply.github.com>

target/rspamd/local.d/worker-controller.inc

@@ -0,0 +1,3 @@
+# documentation: https://rspamd.com/doc/workers/controller.html
+
+bind_socket = "0.0.0.0:11334";