Edit Metadata API endpoint - support empty values

[GPortas]

What this PR does / why we need it:

Extended the Edit Metadata API endpoint:

• This endpoint now allows removing fields (by sending empty values), as long as they are not required by the dataset.
• New sourceInternalVersionNumber optional query parameter, which prevents inconsistencies by managing updates that may occur from other users while a dataset is being edited.

A significant part of the changes involve refactoring the previous logic and addressing missing test coverage (Coveralls reports a +0.1% increase in coverage with these changes). Since I needed to modify the metadata validation logic and its update process, I first had to ensure that the underlying logic was both testable and extensible.

Which issue(s) this PR closes:

• Closes Edit Metadata API endpoint - not allowing empty values #11243

Special notes for your reviewer:

I have identified some areas for improvement in the field validation. For example, as mentioned in my original message on Slack:

It looks like the API currently allows editing multiple fields in a dataset's metadata by setting empty values (e.g. ["", ""]) (https://github.com/IQSS/dataverse/blob/develop/src/main/java/edu/harvard/iq/dataverse/api/Datasets.java#L1188), since the only check performed is that the list is not empty ([]). However, in the case of single fields, it ensures that the string is not empty (https://github.com/IQSS/dataverse/blob/develop/src/main/java/edu/harvard/iq/dataverse/api/Datasets.java#L1191).
Is this intended behavior? Or should the API also check that the values in the list are not empty? This will change in the context of #11243, but I’d like to clarify the current expected behavior.

Finally, I have decided not to implement any changes to the validation logic aside from those necessary for field removal, in order to avoid overextending the scope of this PR and further delaying it. I am willing to create separate issues to apply the enhancements in the future if necessary.

Suggestions on how to test this:

Follow the updated docs for Edit Metadata API endpoint.

Does this PR introduce a user interface change? If mockups are available, please link/include them here:

No

Is there a release notes update needed for this change?:

Yes, attached.

Additional documentation:

None

[coveralls]

coverage: 22.868% (+0.1%) from 22.727%
when pulling 96d84c8 on 11243-editmetadata-api-empty-values
into 9e01018 on develop.

[github-actions]

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