Starting with RabbitMQ 3.13 mqtt.max_session_expiry_interval_seconds
(set in seconds) will replace the previous setting
mqtt.subscription_ttl.
MQTT 5.0 introduces the Session Expiry Interval
feature which does not only apply to subscribers, but also to
publishers.
The new config name mqtt.max_session_expiry_interval_seconds makes it clear
that it also applies to publishers.
Prior to this commit, when mqtt.subscription_ttl was set, a warning got
logged and the value was ignored. This is dangerous if an operator does
not see the warning but relies for example on `mqtt.subscription =
infinity` to not expire non clean session.
It's safer to make the boot fail if that unsupported config name is
still set. A clear error message will be logged:
```
[error] <0.142.0> Error preparing configuration in phase apply_translations:
[error] <0.142.0> - Translation for 'rabbitmq_mqtt.subscription_ttl' found invalid configuration:
Since 3.13 mqtt.subscription_ttl (in milliseconds) is unsupported.
Use mqtt.max_session_expiry_interval_seconds (in seconds) instead.
```
Alternatively, RabbitMQ could translate mqtt.subscription_ttl to
mqtt.max_session_expiry_interval_seconds.
However, forcing the new config option sounds the better way to go.
Once we write MQTT 5.0 docs, this change must go into the 3.13 release notes.
This commit also renames max_session_expiry_interval_secs to max_session_expiry_interval_seconds.
The latter is clearer to users.
ed31a818c3