Maintain history of checkin timestamps

[KCarretto]

Callback timestamps are useful, they can also be used to help identify lapses in our callback coverage (e.g. due to infra issues, blue team actions, etc)

[KCarretto]

If we go the operational logging route we will need to have follow up conversations about how to do it well.

[hulto]

I want to see when imix loses connection based by tags / groups.