Uptime integration add option to retrieve datetime

The Uptime integration now only supports as units of measurement for days, hours and minutes.

Enhance with an option to retrieve to last boot datetime with a timestamp device class for this integration. This is not to be confused with the last boot datetime from the System Monitor integration.

I want this because I don’t want to show: Uptime: 12 h
But something like: Last HA restart: 2 hours ago