docs: add Tile3DLayer example

[AdriSolid]

For: https://app.clubhouse.io/cartoteam/story/133627/add-new-layer-examples

[github-actions]

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https://cartodb-fb-documentation--pr44-adri-3d-tiles-exampl-bc3krqro.web.app

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[borja-munoz]

We should probably host the 3D tiles ourselves instead of using Cesium Ion.

I'm not sure about using this dataset. There is another dataset with New York buildings that can be downloaded using the following link:

https://s3.amazonaws.com/cesiumjs/3DTiles/NewYorkCityGml.zip

But I'm not sure about the license. The best way for us to be covered will be to download the CityGML New York buidlings from here:

https://www1.nyc.gov/site/doitt/initiatives/3d-building.page

And convert them to 3D tiles.

This is out of the scope of this issue, so we are going to keep this PR open until we have a solution.