Render elevation of viewpoints

[ppete2]

tourism=viewpoint are objects where, besides its name, usually also its elevation is an important property. So in my mind it would be a good idea to render its elevation if it's present.

[imagico]

ele on tourism=viewpoint without natural=peak has 4396 uses (about 2 percent).

Like already mentioned in a different context in #1060 (comment) many of these are close to a different feature (like natural=peak, information=guidepost) and duplicate the ele value of that feature. Like here:

https://www.openstreetmap.org/node/2134206537
https://www.openstreetmap.org/node/2396653153
https://www.openstreetmap.org/node/4961680366