With the options in the upstream dovecot module gone the quota support
and its option now live in our downstream module.
The only behavior change this introduces is not setting a global per
user default instead of the previous 100G per user.
Diabling quota support and setting per user quotas now raises an
assertion:
````
Failed assertions:
- Without quota support enabled, per-user quotas cannot be applied to the following accounts:
- lowquota@example.com
Either remove per user quota settings or re-enable `mailserver.quota.enable`.
````
Martin Weinelt
0da8e2b197