Dashboard as a screensaver option for DayDream

**Is your feature request related to a problem? Please describe.**
Android provides a way to show a screensaver view from third party apps. I would love to use this to have a separate view-only dashboard the my tablet could show while idle (and charging). Currently that is possible using Fully Kiosk Browser app as an intermediate step. That does requires a paid app license.

**Describe the solution you'd like**
HA app should advertise as a screensaver option and settings in the app should allow choosing which dashboard should be shown as screensaver, separate from default dash.

**Describe alternatives you've considered, if any**
Using Fully Kiosk Browser as intermediate app works.

**Additional context**
The feature is primarily advertised on Pixel Tablet and autoactivates when docked, if the feature is enabled.