misc: final Rspamd adjustments for v13 (#3599)

* outsource Rspamd ENVs into explicit helper

This will allow us to uniformly source the helper and get the values
from everywhere consistently. This is more than desirable since we will
be using these values not only for the Rspamd setup, but also for DKIM
management and during change-detection.

* integrate Rspamd into changedetection

We outsource one more function to reside in the helper script for Rspamd
so that we can call this function from the Rspamd setup and from the
changedetection functionality too.

* realize deprecation of old commands file for Rspamd

THIS IS A BREAKING CHANGE!

This change realizes the log message: "Using old file location now
(deprecated) - this will prevent startup in v13.0.0" Startup will now
fail.

* added '--force' option to Rspamd DKIM script

* use new helper to get ENVs for Rspamd in DKIM script

* remove the need for linking directories

This was unnecessary, as explained in
https://github.com/docker-mailserver/docker-mailserver/pull/3597#discussion_r1369413599

* Apply suggestions from code review

review by @polarathene

* apply more review feedback from @polarathene

- <https://github.com/docker-mailserver/docker-mailserver/pull/3599#discussion_r1370885519>
- <https://github.com/docker-mailserver/docker-mailserver/pull/3599#discussion_r1370904201>

* update documentation

---------

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

target/scripts/helpers/change-detection.sh

@@ -40,6 +40,12 @@ function _monitored_files_checksums() {
       "${DMS_DIR}/dovecot-quotas.cf"
       "${DMS_DIR}/dovecot-masters.cf"
     )
+
+    # Check whether Rspamd is used and if so, monitor it's changes as well
+    if [[ ${ENABLE_RSPAMD} -eq 1 ]] && [[ -d ${RSPAMD_DMS_D} ]]; then
+      readarray -d '' STAGING_FILES_RSPAMD < <(find "${RSPAMD_DMS_D}" -type f -name "*.sh" -print0)
+      STAGING_FILES+=("${STAGING_FILES_RSPAMD[@]}")
+    fi
   fi
 
   # SSL certs: