Adding more options to dark mode customized options

[langshangyuan]

Currently, we can only configure the dark_mode_background_color option to set the color of empty space which is not occupied by the document. I hope the Sioyek can support dark mode customized options like dark_mode_text_highlight_color, ui_text_color, etc. (Achieve the logical symmetry between light mode and dark mode) These new options allows users to use two different themes under dark mode and light mode to improve the user experience.

[langshangyuan]

The set of options that should be symmetric can be found in the catppuccin sioyek theme.

[ahrm]

We have improved this in the development branch. Now we automatically translate the colors into appropriate colors for the current mode.