GET /file_formats: Expose supported data types and media types

[m-mohr]

For an easier way of understanding the exposed file formats, it would be helpful to give some more information on what they offer.

Right now we just expose the "gis_data_type" (raster, vector, table, ...), but it would be great to get some more information so that clients can easily hint at potential improvements, e.g. scaling.

Interesting could be:

• Media type (e.g. image/png)
• Data type (e.g. uint8 for PNG)
• Max number of bands (e.g. 1/3/4)