[OPR] Only metadata fields that require a human review should be required by the OPR, others optional.

[jh-RLI]

Description of the issue

We implemented a wee working version of the Open Peer Review. The review process itself is now somewhat stable (stable enough) and we have to trim down the time an average review takes.

Relevant user interaction:

Less time-consuming

• Accept a field

More time-consuming

• Suggest a field
• Deny a field

Very time-consuming

• Any of the actions above applied on a lot of fields.

Ideas of solution

Make fields that do not require a human reviewer optional and indicate that to the user.

Only check for required fields to be able to submit or finish a review.

Workflow checklist

• [ ] I am aware of the workflow in CONTRIBUTING.md