[Feature Request]: Add Gruvbox themes.

[Cyanide-1]

Guidelines

• I have searched the issue tracker for open and closed issues that are similar to the feature request I want to file, without success.
• I have searched the documentation for information that matches the description of the feature request I want to file, without success.
• This issue contains only one feature request.

Problem Description

Add the gruvbox dark and gruvbox light themes as an option for selectable themes.

Proposed Solution

Add both gruvbox dark and gruvbox light themes.

Alternatives Considered

N/A

Issue Labels

improvement to existing feature, new optional setting

Additional Information

There is a color pallet for gruvbox here (scroll a little bit for the color pallet): https://github.com/morhetz/gruvbox

examples of various gruvbox themes as a reference:
https://github.com/Fausto-Korpsvart/Gruvbox-GTK-Theme
https://github.com/sachnr/gruvbox-kvantum-themes
https://github.com/SylEleuth/gruvbox-plus-icon-pack