[Clock] Update system timezone via ConfigDB

[fastiuk]

hld #1219
closes #1171

This PR brings functionality that allows us to update the system timezone by writing to the timezone field of the DEVICE_METADATA table of ConfigDB.
The clock CLI implemented in #2793 uses that functionality as the backend.

[linux-foundation-easycla]

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• ✅ login: fastiuk / name: Yevhen Fastiuk (cfd6dc1, 5c75858, 3ca69ee, ae2f499)

[liat-grozovik]

@fastiuk please update the PR description and the PR subject. this PR is not for CLI but for a backend.

[yxieca]

The fact that this code in hostcfgd is needed, does that imply that the BIOS clock is NOT synchronized with the OS settings? Which further implies that during reboot, the clock would be wrong until hostcfgd fixes the date/time? This is not safe for upgrades.

[yxieca]

Why do we need this change?

[fastiuk]

The fact that this code in hostcfgd is needed, does that imply that the BIOS clock is NOT synchronized with the OS settings? Which further implies that during reboot, the clock would be wrong until hostcfgd fixes the date/time? This is not safe for upgrades.

No, it doesn't. The code reflected here is to update the system timezone, and it doesn't touch system time.
I would say, even more, changing the timezone is a permanent change, which will persist after a reboot, because timedatectl writes timezone to /etc/timezone.

[fastiuk]

Why do we need this change?

Which one, I don't see any code snippet

[fastiuk]

Ping here

[yxieca]

Please confirm if there are tabs in the diff. If so, please change to white spaces.

[fastiuk]

Please confirm if there are tabs in the diff. If so, please change to white spaces.

no tabs in diff