Bypass internal load_stac, if there is no processing between CWL and export_workspace

[EmileSonneveld]

This would avoid small differences getting introduced like pixel shifts or losing metadata.

[EmileSonneveld]

@soxofaan This schema show a bit the possible process graphs we talked about.

[EmileSonneveld]

Relevant discussions here: Open-EO/openeo-processes#485