fix(changedetector): Use service reload commands instead of supervisorctl restart <service> (#2947)

With `reload` a change detection event during local testing can be processed in less than a second according to logs. Previously this was 5+ seconds (_plus additional downtime for Postfix/Dovecot to become available again_).

In the past it was apparently an issue to use `<service> reload` due to a concern with the PID for wrapper scripts that `supervisorctl` managed, thus `supervisorctl <service> restart` had been used. Past discussions with maintainers suggest this is not likely an issue anymore, and `reload` should be fine to switch to now 👍 

---

**NOTE:** It may not be an issue in the CI, but on _**local systems running tests may risk failure in `setup-cli.bats` from a false positive**_ due to 1 second polling window of the test helper method, and a change event being possible to occur entirely between the two checks undetected by the current approach.

If this is a problem, we may need to think of a better way to catch the change. The `letsencrypt` test counts how many change events are expected to have been processed, and this could technically be leveraged by the test helper too.

---

**NOTE:** These two lines (_with regex pattern for postfix_) are output in the terminal when using the services respective `reload` commands:

```
postfix/master.*: reload -- version .*, configuration /etc/postfix
dovecot: master: Warning: SIGHUP received - reloading configuration
```

I wasn't sure how to match them as they did not appear in the `changedetector` log (_**EDIT:** they appear in the main log output, eg `docker logs <container name>`_).

Instead I've just monitored the `changedetector` log messages, which should be ok for logic that previously needed to ensure Dovecot / Postfix was back up after the `restart` was issued.

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Commit history:

* chore: Change events `reload` Dovecot and Postfix instead of `restart`

Reloading is faster than restarting the processes.

Restarting is a bit heavy handed here and may no longer be necessary for general usage?

* tests: Adapt tests to support service `reload` instead of `restart`

* chore: Additional logging for debugging change event logs

* fix: Wait on change detection, then verify directory created

Change detection is too fast now (0-1 seconds vs 5+).

Directory being waited on here was created near the end of a change event, reducing that time to detect a change by the utility method further.

We can instead check that the directory exists after the change detection event is completed.

* chore: Keep using the maildir polling check

We don't presently use remote storage in tests, but it might be relevant in future when testing NFS.

This at least avoids any confusing failure happening when that scenario is tested.

target/scripts/check-for-changes.sh

@@ -56,13 +56,11 @@ function _check_for_changes
     _ssl_changes
     _postfix_dovecot_changes
 
-    # While some config changes may be properly applied by Postfix or Dovecot
-    # via their 'reload' commands; some may require restarting?:
-    _log_with_date 'debug' 'Restarting services due to detected changes'
+    _log_with_date 'debug' 'Reloading services due to detected changes'
 
     [[ ${ENABLE_AMAVIS} -eq 1 ]] && _reload_amavis
-    supervisorctl restart postfix
-    [[ ${SMTP_ONLY} -ne 1 ]] && supervisorctl restart dovecot
+    postfix reload
+    [[ ${SMTP_ONLY} -ne 1 ]] && dovecot reload
 
     _remove_lock
     _log_with_date 'debug' 'Completed handling of detected change'
@@ -113,6 +111,7 @@ function _postfix_dovecot_changes
   || [[ ${CHANGED} =~ ${DMS_DIR}/dovecot-quotas.cf   ]] \
   || [[ ${CHANGED} =~ ${DMS_DIR}/dovecot-masters.cf  ]]
   then
+    _log_with_date 'trace' 'Regenerating accounts (Dovecot + Postfix)'
     [[ ${SMTP_ONLY} -ne 1 ]] && _create_accounts
   fi
 
@@ -126,6 +125,7 @@ function _postfix_dovecot_changes
   || [[ ${CHANGED} =~ ${DMS_DIR}/postfix-relaymap.cf      ]] \
   || [[ ${CHANGED} =~ ${DMS_DIR}/postfix-sasl-password.cf ]]
   then
+    _log_with_date 'trace' 'Regenerating relay config (Postfix)'
     _rebuild_relayhost
   fi
 
@@ -138,6 +138,7 @@ function _postfix_dovecot_changes
   if [[ ${CHANGED} =~ ${DMS_DIR}/postfix-accounts.cf ]] \
   || [[ ${CHANGED} =~ ${DMS_DIR}/postfix-virtual.cf  ]]
   then
+    _log_with_date 'trace' 'Regenerating vhosts (Postfix)'
     _create_postfix_vhost
   fi