Solve the issue with the STAC collection creation

[gfenoy]

We added a comment about the raster extension, which should be activated in the stac step.

The lines asserting its presence have been commented on.

We have made tests setting the with_raster parameter to the rio_stac.stac.create_stac_item invocation and confirmed that it works perfectly fine with the two commented lines uncommented.

If it sounds good, we suggest updating this part, too. We can create another PR for this to continue on this one.

We are waiting for you to confirm that we would like to activate the raster_extension per default for every CWL workflow.

We may also consider passing a given environment variable to define which extension should be used from the stac step.

Let us know what you think.