Add `treatMissingDataOverride` to `alarmDefaults`

[jackrein]

Feature scope

ALL

Describe your suggested feature

To configure an alarm's treatMissingData field, it's required to use the treatMissingDataOverride on each alarm.

For cases where the default value (MISSING) is not desired for any alarm, it would be nice to have the ability to specify in the alarmFactoryDefaults for all alarms.