Add ability to hide the UV attribute

[AndrewPDeer]

Missing capability:

It is not currently possible to hide the UV index without turning off all the attributes with "show_attributes: false"
Using "show_sun: false" does not do it either.

Proposed solution:

Add boolean "show_uv" to the list of possible yaml commands and (ideally) this same capability added to the UI.
Update the documentation accordingly.

Tested with version: 2.4.11

[hfalk]

This would be a very nice enhancement 🤩

[folfy]

I first thought showing the UV index is a new feature of weather-chart-card, since it suddenly popped up since my last round of updating everything, but seems it might be actually a change in the underlying weather entity (using the default Met.no).

Seems to be rather easy to implement, might have a look myself on the weekend, and create a PR.