Remove cars from SSM that haven't been "seen" in X months

[davidfsmith]

The current live version of DREM shows over 1K cars as offline, some of these will be duplicate activations when cars have been flashed and re-DREM'd multiple times.

We should track the cars original hostname when creating a new activation so we can start to create a full car history (longer term) and also so we can remove outdated instances of the car from SSM.

Using the original hostname of the car also allows us to start tracking usage per physical car (rather than usage per hostname) over time so we can add in the concept of a car history / maintenance log

[MarkRoss-Eviden]

this would be good but ideally configurable (e.g. be able to set number of dormant months before removal) for those of us having corporate instances, as we may not use our cars for months.