Implement DSpace REST API workflow

[rhigman]

This will sit alongside the DSpace SWORDv2 workflow. For each individual platform, we can choose which route we select. SWORDv2 remains useful as a legacy integration, but the new REST API is preferred from DSpace v7 onwards.

Switch over Cambridge University Library pilot repository to REST API workflow once completed.

Recommended Python client library for the REST API is https://github.com/the-library-code/dspace-rest-python. It is in active development and there may be contributions we can usefully make.