Allow for showing time zone in time/date widget on dock

### Feature Description

This could either be implemented as a switch allowing for toggling showing the time zone or there could be an option to set a custom time format, in the same way you can set a custom date format.

### Use Case

It's useful if you change time zones because of travel or for when the clocks change due to DST.

### Compositor(s)

- [ ] All compositors
- [ ] Niri
- [ ] Hyprland
- [ ] MangoWC (dwl)
- [ ] Sway
- [ ] Other (specify below)

### Proposed Solution

_No response_

### Alternatives/Existing Solutions

_No response_