fix: Workaround postconf write settling logic (#2998)

* fix: Workaround `postconf` write settle logic

After updating `main.cf`, to avoid an enforced delay from reading the config by postfix tools, we can ensure the modified time is at least 2 seconds in the past as a workaround. This should be ok with our usage AFAIK.

Shaves off 2+ seconds roughly off each container startup, reduces roughly 2+ minutes off tests.

* chore: Only modify `mtime` if less than 2 seconds ago

- Slight improvement by avoiding unnecessary writes with a conditional check on the util method.
- Can more comfortably call this during `postfix reload` in the change detection cycle now.
- Identified other tests that'd benefit from this, created a helper method to call instead of copy/paste.
- The `setup email restrict` command also did a modification and reload. Added util method here too.

* tests(fix): `mail_smtponly.bats` should wait for Postfix

- `postfix reload` fails if the service is not ready yet.
- `service postfix reload` and `/etc/init.d/postfix reload` presumably wait until it is ready? (as these work regardless)

* chore: Review feedback - Move reload method into utilities

test/helper/common.bash

@@ -28,6 +28,14 @@ function _default_teardown() {
   docker rm -f "${CONTAINER_NAME}"
 }
 
+function _reload_postfix() {
+  local CONTAINER_NAME=${1:-${CONTAINER_NAME}}
+
+  # Reloading Postfix config after modifying it in <2 sec will cause Postfix to delay, workaround that:
+  docker exec "${CONTAINER_NAME}" touch -d '2 seconds ago' /etc/postfix/main.cf
+  docker exec "${CONTAINER_NAME}" postfix reload
+}
+
 # -------------------------------------------------------------------
 
 # @param ${1} program name [REQUIRED]