Stac item extensions

[ValentinaHutter]

One thing I noticed about the sen2like outputs recently, is that the stac-items do not give any information about scale and offset of the bands. In the MTD.json there seems to be an offset but no scale. The stac items could be updated with the raster-extension: https://stac-extensions.github.io/raster/v1.1.0/schema.json

An example would look like this:

    "raster:bands": [
        {
          "nodata": 0,
          "data_type": "uint16",
          "spatial_resolution": 10,
          "scale": 0.0001,
          "offset": -0.1
        }
      ],

This would allow automatic applying of scale and offset when loading the data with stac - so it might be useful for some users :) (I currently apply scale and offset manually, and others probably do the same, so this is just a suggestion to include in a future update.)