[BUG] Wrong assay and study paths in RO-Crate export

[floWetzels]

The identifiers of assays and studies in the json object produced by the RO-Crate export sometimes contain invalid paths. In particular, they sometimes start with a # symbol. This is then not valid RO-Crate.

Furthermore, the RO-Crate specification states that paths SHOULD end in a / symbol, which we should probably also adapt.

To Reproduce
Go to the Metabolights338_ARC from the datahub. Export the RO-Crate in the same way the CI does (only tested with CI output).