Make tz selection deliberate

[h8d13]

Instead of over complex like I tried in #4002

This is a much simpler approach we set the fallback in args.py and make it mandatory in the menu.
Again this to address lots of logs that get PGP verif errors because TZ was not set.

[Torxed]

I'm not sure I understand what the original problem was?
When I'm lazy I usually just stick with the default UTC and it works fine, unless the hardware clock is way off - but that's more an issue of it being off than what time zone I picked?

[h8d13]

Just because I see of lot of error logs than yeah its hardware clock (which also gets reset on dead CMOS), so i thought making it explicit choice + showing RTC clock originally (previous PR #4002)

[Torxed]

hmm, well NTP should make stuff "just work", as it should happen before archinstall starts strapping in packages. And a timezone shouldn't be needed?

[h8d13]

My thought was that I could be dead (the service, happens sometimes) or disconnected for offline installs with cached files, so time being wrong there would cause pgp errors.

But yeah I do see how it's technically a non-problem for regular usage.