Py3DTiles - Make the number of tiles an argument of the tilers

[jailln]

Depending on the use case, we want to generate 3D Tiles tilesets with different number of tiles. Use cases include analyses and comparisons for articles, demonstrations, debugging, etc.

Currently, the number of tiles in the tileset depends on an argument of the kd tree creation function that specifies the maximum number of city object per tile. This value is hardcoded in the tilers (e.g. in CityTiler).

We should allow the user to specify how many tiles should be in the tileset and compute the maximum number of city objects per tiles from this value and from the total number of city objects.

Note: this issue is opened here since it is not possible to open issues on our fork of py3dtiles.