This introduces functionality to manage local Dovecot users utilizing a
static `vmail` system user and a flat password file.
Key changes:
- Added `dovecot_users` configuration list to defaults.
- Implemented creation of `vmail` user and group (uid/gid 5000).
- Added logic to generate a random security token using `pwgen` to prefix
user passwords.
- Created `auth-dovecot-users.conf.ext` and `dovecot-users.j2` templates
to handle `passwd-file` authentication.
- Updated `10-auth.conf` to include the new local users configuration.
- Updated README with usage instructions and token details.
Luciano Giacchetta
dfd5d89905