Support different processing version for Sentinel-2

[konstntokas]

Sentinel-2 products from different time ranges can have different processing version. There are temporal overlaps where tiles are duplicated with different processing versions.

This is already handles by xcube-stac. However, the processing version is missing in the EOPF STAC items (see issue: EOPF-Sample-Service/eopf-stac#28)

2 Options:

• wait for update in the STAC API -> shift to 2. release.
• read out processing version from path -> can be implemented now.