Fix sorting of dataset drafts and minor versions when sorting by "newest first"

[vera]

What this PR does / why we need it:

This PR fixes an issue where draft and minor versions of datasets were sorted using the release timestamp of their most recent major version.
This caused newer drafts or minor versions to appear incorrectly alongside their corresponding major version, instead of at the top, when sorted by "newest first". This affects the search results page and the "My data" page, both of which are sorted by newest by default.
Sorting now consistently uses the last update timestamp for all dataset versions (draft, minor, and major).

See bug description with screenshot etc in #11178

Which issue(s) this PR closes:

• Closes Bug?: unexpected sorting of results when sorting by "newest first" (Search + My Data) #11178

Special notes for your reviewer:

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Suggestions on how to test this:

I've added a test that can be run with: mvn test -Dtest="DataRetrieverApiIT#testRetrieveMyDataAsJsonStringSortOrder"

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

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

I think it would be good to include a release note for this bug fix, since it affects the default sorting of datasets on the search results and "My data" page. I've added a release note as part of this PR

Additional documentation:

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[pdurbin]

TODO: Review the sorting rules from https://docs.google.com/document/d/1DWsEqT8KfheKZmMB3n_VhJpl9nIxiUjai_AIQPAjiyA/edit?usp=sharing and update this comment.