Popup to copy plugin settings when using nix

### Feature Description

There is already a feature to copy temporary config from the UI, in order to convert to nix.
It would be great to have the same feature for plugin settings too.

### Use Case

_No response_

### Compositor(s)

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

### Proposed Solution

_No response_

### Alternatives/Existing Solutions

_No response_

Start by locating the existing UI feature that copies temporary config for conversion to nix, then trace how plugin settings are represented and exposed in the UI. Done means an equivalent popup can copy plugin settings for nix users across the supported compositors.

Written by the indexing model from the issue text.