Nicer TZ config & help

[mcspr]

ref. #2544

It would be great if "Time Zone" was a drop down list. Since it's quite hard to figure out how to set POSIX TZ
(Values from https://github.com/esp8266/Arduino/blob/master/cores/esp8266/TZ.h work, but usability...)
(Time is very important to me because I need a scheduler.)

I suppose link could go to some kind of table file looking like this instead of a scary header file

• https://github.com/nayarsystems/posix_tz_db/blob/master/zones.csv

tzdata package data probably needs to be updated to 2022 values, but parsing is pretty much just reading the last line of a /usr/share/zoneinfo/* file

> tail -1 /usr/share/zoneinfo/Africa/Abidjan
GMT0

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Just solving TZ issue for the time being. Having a handmade tz handling does not seem like a good idea, and integrating something external needs to be pretty slim.
(to configure something that needs to be done at most once)