Add support to retrieving properties on the mvt_elastic provider

[doublebyte1]

Is your feature request related to a problem? Please describe.
The current implementation of the MVT-elastic provider does not support publishing the properties associated to the geometries. It is worth noting that attribute based styling on client side, is one of the main arguments for preferring vector tiles over raster tiles. If a client can only retrieve the geometries, its analytical and visualisation capabilities are severely limited.

Describe the solution you'd like
Providing the properties along with the geometries.

Describe alternatives you've considered
Use the mvt-proxy or mvt-tippecanoe providers.