Add option to time picker to revert to dashboard default

**Why is this needed**: Currently in v11.5.0 (f7a938db9a) there seems to be no easy way to reset the time picker to the dashboard default after for example selecting a custom value or zooming into a time graph. I could open up the time picker again and manually select the default but I might not even know what the default is. In Grafana v11.2 if you only had one default dashboard, it was possible to simply click on "Home" on the top left and the picker would revert to the dashboard default. As of v11.5 this is no longer possible.  **What would you like to be added**: A simple deselector thingy like an X to make it super easy to reset to the dashboard default. I'm picturing something like this:  Klick the X and the time picker resets. **Who is this feature for?** People who use my dashboards are not that tech savy and need an easy option for something like this.