Replace daily timer-based message expire script
with Dovecot quota-warning-triggered cleanup.
When a user reaches 90% of their mailbox quota
Dovecot calls the new script which removes the largest and oldest messages
until usage drops below 80%.
The daily `chatmail-expire` service now only
handles deletion of inactive user mailboxes.
Similar data is already generated by fsreport
available for the relay operator
and metrics for prometheus are generated by mtail.
Closes <https://github.com/chatmail/relay/issues/431>
This change adds XDELTAPUSH capability.
Delta Chat clients detecting this capability
can set /private/devicetoken IMAP metadata
on the inbox to subscribe for Apple (APNS)
notifications.
Notifications are implemented in a new
`chatmail-metadata` service
which handles requests to set /private/devicetoken
IMAP metadata from Delta Chat clients
and /private/messagenew requests from
push_notification_lua script.
To avoid sending notifications for
MDNs, webxdc updates and Delta Chat sync messages,
messages with Auto-Submitted header are ignored
by setting $Auto keyword (flag) on them in Sieve script
and skipping such messages in push_notification_lua script.
Outgoing messages are also ignored.
