dovecot: update templates according to bullseye's defaults

dovecot/templates/conf.d/10-auth.conf.j2

dovecot/templates/conf.d/10-mail.conf.j2

dovecot/templates/conf.d/10-master.conf.j2

dovecot/templates/conf.d/10-ssl.conf.j2

dovecot/templates/conf.d/15-lda.conf.j2

dovecot/templates/conf.d/20-imap.conf.j2

dovecot/templates/conf.d/20-lmtp.conf.j2

dovecot/templates/conf.d/20-managesieve.conf.j2

dovecot/templates/conf.d/90-sieve.conf.j2