CmdPal: Add theme mode to follow Windows theme

[jiripolasek]

Description of the new feature / enhancement

The Command Palette app theme now has three options: System, Light, and Dark. However, since the Command Palette is essentially a system launcher, we may want to align its behavior with the Start menu and other system surfaces that follow the Windows theme mode.

Scenario when this would be used?

UX

Supporting information

No response