Improve 3dtiles filename handling

[mattiagiupponi]

Is your feature request related to a problem? Please describe.
At the moment the import workflow, expects that the 3dtiles zip file contains a file named tileset.json, but from the specification, the tileset file, can have any name

Describe the solution you'd like
We should improve the import workflow to allow the user upload a 3dtiles zip with any name for the tileset json file.
This will need a small validity check on the json file found in the folder. This validation must be done also on the GeoJson handler so we dont risk to mix the handlers