dovecot-example.conf: Make it clear mail_log_group_events is boolean.
dovecot-example.conf: Make it clear mail_log_group_events is boolean.

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branch : HEAD

jwm/dovecot-notmuch,jwm/dovecot-notmuch,jkerihuel/dovecot,jkerihuel/dovecot,jkerihuel/dovecot,jwm/dovecot-notmuch,jwm/dovecot-notmuch,jwm/dovecot-notmuch,jkerihuel/dovecot,jkerihuel/dovecot