Allow customizing date format in dank bar when bar is on the side

### Feature Description

Allow customizing date format in dank bar when the bar is on the side, or at least the ability to show the day of week (Mon - Sun).

The date format can be changed when the bar is on the bottom, but when it is on the side the setting has no effect.

### Use Case

I rely on knowing the day of the week to keep track of the date.

### Compositor(s)

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

### Proposed Solution

_No response_

### Alternatives/Existing Solutions

_No response_