I've added a p/r that implements a 'date+time' metric https://github.com/openvehicles/Open-Vehicle-Monitoring-System-3/pull/946

I've also added a comment that reads as follows:

One discovery I made while implementing this was that time_t is a 32bit number. It seems when we move to the 5.0+ framework this will be fixed in the esp32 libraries, but we will still need to implement a separate metric class for 64 bit time_t values. I'm thinking that an easy way to do it, since the underlying persist mechanism is 32bit, would be to have "_high" suffix a store the high bit as a "separate" metric. Should I do it with this patchset? I can implement the separate metric class and put in #ifdefs for when the time_t value is 64bit.

Thoughts on this?? It also highlights the importance of pushing forwards with the new frameworks and filling in the gaps for that.

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