Doc: Document HarmonyOS sensor permissions

The accelerometer and gyroscope require the
ohos.permission.ACCELEROMETER and ohos.permission.GYROSCOPE permissions
respectively. The other sensors provided by the HarmonyOS backend do not
require any permission.

Document this in the platform specific notes.

Pick-to: 6.12
Task-number: QTBUG-146844
Change-Id: I61af51886fefc66b508b0bf8365bc4c99c841b60
Reviewed-by: Liang Qi <liang.qi@qt.io>
Reviewed-by: Shuang Zhu <sol.zhu@qt.io>
Reviewed-by: Seokha Ko <seokha.ko@qt.io>