RO-Crate submission API

[fbacall]

Idempotent API endpoint for POSTing a Workflow RO-Crate that will either:

• Create a new workflow
• Add a version to an existing workflow
• Do nothing because the workflow & version were already registered

...based on a source URL & version name contained within the RO-Crate metadata.

This makes it easy to integrate into e.g. GitHub actions, because no state has to be tracked.