Facet license missing

[jrhoads]

Purpose

This pull request introduces a new facet for licenses in the DataCite DOIs controller that accounts for missing values. It enhances the faceting capabilities by enabling the retrieval of license identifiers along with an additional entry for licenses that are missing, thus providing a more comprehensive view of the licenses associated with DOIs.

Key Modifications:

1. New Facet Method:

   • Introduced facet_by_license_and_other method in the Facetable concern. This method aggregates license data and includes an additional entry for licenses that are missing.

2. Updates in Controller:

   • Modified the DataciteDoisController to include the new licenses_with_missing facet, mapping it to the newly created method.
   • Updated the facets_to_bucket_path to accommodate the new facet.

3. Model Changes:

   • Altered the Doi model to define the licenses_with_missing facet with a query for terms that includes a missing condition.

4. Testing Additions:

   • Added a new request spec to validate the functionality of the licenses_with_missing facet, confirming that it returns expected results when a DOI does not have a specified license.

Technical Details:

• The new facet_by_license_and_other method consolidates the logic of faceting licenses while adding functionality to handle and display missing license identifiers.
• The query for licenses_with_missing in the Doi model uses { "missing": "__missing__" } to effectively capture entries lacking a specified rights identifier.
• The added specs ensure that the API correctly returns results with missing license values when requested, enhancing the robustness of the data retrieval process.

This PR aims to improve the usability and accuracy of license data in the DataCite system, allowing users to better understand the licensing landscape of DOIs.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

• New feature (non-breaking change which adds functionality)

• Breaking change (fix or feature that would cause existing functionality to change)

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