implement or deviate the control/max-alarm-status-changes leaf

[jktjkt]

In the alarm control, there's a leaf called /alarms/control/max-alarm-status-changes which is supposed to control the length of some alarm status history list. Currently we do not implement that leaf, but there's no deviation which would say that it isn't supported, and the default value is kept at the RFC default of 32.

This needs triaging; I have no idea how useful that leaf is. As a minimum, however, its default value should be augmented, or it should be marked as not supported.