Promote export workspace to default

[dsamaey]

Remove the experimental flag and make it default.
Make sure to communicate the changes and impact (proper use of the "merge" property ?) to users.

[jdries]

To be clear:
for jobs without export workspace, the default should be to stay on stac-version: 1.0, and users can opt-in to use 1.1.
When export-workspace is used, the default can be 1.1, because 1.0 is basically broken in that case.