refactor: logrotate setup + rspamd log path + tests log helper fallback path (#3576)

* simplify `_setup_logrotate`

* adjust Rspamd's log file and improve it's management

* add information to docs about Rspamd log

* update log query helper to allow another file location

* bail in case `LOGROTATE_INTERVAL` is invalid

---------

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

target/scripts/startup/setup.d/security/rspamd.sh

@@ -7,6 +7,7 @@ function _setup_rspamd() {
     __rspamd__log 'trace' '----------  Setup started  ----------'
 
     __rspamd__run_early_setup_and_checks      # must run first
+    __rspamd__setup_logfile
     __rspamd__setup_redis
     __rspamd__setup_postfix
     __rspamd__setup_clamav
@@ -101,6 +102,20 @@ function __rspamd__run_early_setup_and_checks() {
   fi
 }
 
+# Keep in sync with `target/scripts/startup/setup.d/log.sh:_setup_logrotate()`
+function __rspamd__setup_logfile() {
+  cat >/etc/logrotate.d/rspamd << EOF
+/var/log/mail/rspamd.log
+{
+  compress
+  copytruncate
+  delaycompress
+  rotate 4
+  ${LOGROTATE_INTERVAL}
+}
+EOF
+}
+
 # Sets up Redis. In case the user does not use a dedicated Redis instance, we
 # supply a configuration for our local Redis instance which is started later.
 function __rspamd__setup_redis() {