add blockchain/linked list history to higher-level products

**Is your feature request related to a problem? Please describe.**
Currently, the file names are the only means to identify the contents of a file. Often, even inspection of the data cannot unambiguously trace their origin. However, for scientific purposes the user might need to verify the data integrity. Especially in automated setups, filenames are not sufficiently robust to ensure that the contents are what the user expects them to be.

**Describe the solution you'd like**
I could imagine a git branch/blockchain/linked list/... -like structure. It should be apparent what version of the input data and what version of cryoswath was used at different stages. At least, a l4-file should identify its parent l3-file.

No files or tests are named. Start by tracing how l3-files and l4-files are produced and where their metadata is defined; clarify the provenance model and how input-data and CryoSwath versions should be recorded before implementation. Done means higher-level products can identify their parent data and processing versions unambiguously.

Written by the indexing model from the issue text.