The new function can
1. update/append
2. update/prepend
3. initialize if non-existent
options in `/etc/postfix/main.cf` in a safe and secure manner. When the
container is improperly restarted, the option is not applied twice.
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Co-authored-by: Casper <casperklein@users.noreply.github.com>
Co-authored-by: Brennan Kinney <5098581+polarathene@users.noreply.github.com>