Add Plasma 6 icons

[Kodehawa]

Title. Plasma 6 requires the icon theme to define the plasmashell icons instead of the Plasma theme now. Applying this icon theme on Plasma 6 causes plasmashell icons to look pretty odd (which is the case with most icon themes as of now), but it doesn't break compatibility with Plasma 5, so it doesn't hurt to add the new icons now.

[Kodehawa]

Tela bug report for this: vinceliuice/Tela-icon-theme#261

Post from KDE folk for impl: https://pointieststick.com/2023/08/12/how-all-this-icon-stuff-is-going-to-work-in-plasma-6/