Dovecot master accounts can now be configured in DMS via `setup.sh`.
A master account is useful for administration purposes, or to perform mailbox backups of every user account over IMAP.
Upstream Docs: https://doc.dovecot.org/configuration_manual/authentication/master_users/
Co-authored-by: Casper <casperklein@users.noreply.github.com>
Co-authored-by: Brennan Kinney <5098581+polarathene@users.noreply.github.com>
