add interactive osd to switch power profiles

To trigger the OSD, press Meta+B. It should also work with the power mode function key that some laptops have, though I'm not sure I got the keycode right as I don't have one myself. Can someone who has such a device test this? @apol @adridg

For testing in a development session, you may need to run the install sessions script (cd kde6/build/plasma-workspace; sudo ./login-sessions/install-sessions.sh) after building so the service file is copied to where DBus expects it.

There's a lot of copy-paste from the KScreen OSD so eventually we might want to make it some sort of reusable component.

FEATURE: 469487 FIXED-IN: 6.0