Fix UI error - create Crossref DOI failed

[jsjiang]

Create Crossref DOI failed on create simple and with error message:

1. Create simple identifier on test Crossref DOI shoulder (doi:10.15697/) failed as the input data used DataCite format Error message:

   Identifier could not be created as submitted: error: bad request - error="ValidationError(["Registration with Crossref requires Crossref metadata supplied as value of element 'crossref'. Received metadata: {'datacite.creator': 'test creator', 'datacite.title': 'test title 2', 'datacite.publisher': 'test publisher', 'datacite.publicationyear': '2024', 'datacite.resourcetype': 'Book'}"])" Metadata: {'datacite.creator': 'test creator', 'datacite.publicationyear': '2024', 'datacite.publisher': 'test publisher', 'datacite.resourcetype': 'Book', 'datacite.title': 'test title 2'}

2. Create advanced identifier on test Crossref DOI shoulder (doi:10.15697/) failed because the "custom remainder" field is not provided. The "custom remainder" field is actually optional. Error message:

   Optional: Enter a custom remainder (suffix)
   This combination of characters cannot be used as a remainder.

Find out:

• who use UI to perform Crossref DOI registration and how often
• any needs to support Crossref registration In EZID UI
• how to fix the problem

[jsjiang]

Note:

• Based on the EZID Crossref Support Notes, "Support Crossref DOIs in UI registration form" may not have been implemented.