Add mandatory RO-Crate metadata when exporting

[elichad]

[in progress during a hackathon this week]

Problem:

Galaxy RO-Crates do not fully comply with the Workflow Run Crate specification.

Changes:

• added tests which use rocrate-validator to validate generated RO-Crates, both for history export (base RO-Crate spec) and workflow invocation export (Workflow Run Crate spec)
• added missing mandatory metadata - name, description, and license in the root dataset of the crate.
  • for history export, it seems difficult to set a useful (non-ambiguous) name, I don't know if it's possible to access the name of the history at this place in the code

Still in progress:

• checking over existing test functions to see if some can be removed as they might be covered by the validator

How to test the changes?

(Select all options that apply)

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

License

• I agree to license these and all my past contributions to the core galaxy codebase under the MIT license.