Add PLASMA_MOBILE_LOCAL_KAUTH_INSTALL CMake option to redirect KAuth
helper executables, D-Bus service files, and polkit policy files into
CMAKE_INSTALL_PREFIX instead of hardcoded /usr paths.
Guard KF6Auth find_package calls in helper subdirectories with
if(NOT TARGET KF6::AuthCore) to avoid re-running find_package after
the top-level override, which would revert generated service Exec
paths back to /usr/libexec/kf6/kauth.
I prefer create MR now to avoid biggest merge request.
It add minimalist implementation:
- First configuration of Waydroid
- Stop / Start Waydroid session
- Configure properties of Waydroid
- Display current ip of Waydroid
| Not installed | First initialization | initializing | SessionNotStarted | SessionStarting | SessionStarted |
| ------ | ------ | ------ | ------ | ------ | ------ |
|  |  |  |  |  |  |
Linked to https://invent.kde.org/teams/plasma-mobile/issues/-/issues/307
**Note for Reviewer**: In my local environment, i need to add manually the KAuth files otherwise polkit not recognize the implementation.
```
sudo cp ~/kde/usr/share/dbus-1/system-services/org.kde.plasma.mobileshell.waydroidhelper.service /usr/share/dbus-1/system-services/
sudo cp ~/kde/usr/share/dbus-1/system.d/org.kde.plasma.mobileshell.waydroidhelper.conf /usr/share/dbus-1/system.d/
sudo cp ~/kde/usr/share/polkit-1/actions/org.kde.plasma.mobileshell.waydroidhelper.policy /usr/share/polkit-1/actions/
```
