Datacite xml improvements

[qqmyers]

What this PR does / why we need it: This PR updates the XML sent to DOI providers to be richer and more consistent with what is in the OpenAire export. There are differences (most obviously, the code here works for draft datasets and files which are not handled by the OpenAire exporter), most are probably subtle but @jggautier or others may wish to look at/comment on the list of changes I've tried to track in this doc.

This is nominally one of 2 PRs related to DOI metadata - the other will be a change to the citation metadatablock to add a relationshipType to the field(s) where we expect to report the relationships to DataCite/etc.

Which issue(s) this PR closes: Probably closes #5889 when combined with the relationshipType PR. Closes #

Special notes for your reviewer: The PR includes some refactoring of our XML generation code that is common with the DDI export. @poikilotherm's idea of generating a model from the DataCite schema might be a good next step (hopefully easier given the code here to get the content needed).

Suggestions on how to test this: QDR is testing this code now. There is one new test in addition to the existing ones - it could/should be expanded to test a dataset with more of the metadata that is covered by the new code - possibly just reading in one of the ~complete dataset examples we have. Verification that the result matches the DataCite schema is included.

Does this PR introduce a user interface change? If mockups are available, please link/include them here: only changes the XML sent to the DOI provider which is also exposed as a metadata export. The change makes the OpenAire export somewhat redundant, but as noted above, there are differences which may need to be kept.

Is there a release notes update needed for this change?: yes - will create once the set of changes (in the doc above) is reviewed. Probably should be combined with the citation block change if that can be created in time for the same release.

Additional documentation: