Enhancement: validate RO-Crates

[rsirvent]

The current compatibility with RO-Crates of WorkflowHub is a bit weak:

• No errors are provided to the user when the input RO-Crate is wrong (just a generic error 500).
• Workflow versions cannot be updated from RO-Crate (see issue Add "Upload RO-Crate" option to new version form #1959 ).

I would like to suggest that you integrate the RO-Crate validator to these processing of RO-Crates, so WFHub can ensure RO-Crates are valid and WFHub only has to print to the user any errors the validator reports.

https://github.com/crs4/rocrate-validator

I would like to hear opinions on this also from @stain and @simleo.

[simleo]

I think there's been talk about something like this at one of the WorkflowHub meetings