Follow-up to versioned release schema updates

[jpmckinney]

Follow-up to #738

In make_versioned_release_schema.py:

• Account for minLength when replacing sections with e.g. StringNullVersioned
• Ensure that title, description, merging properties, etc. are removed in a single, final pass.
• Add more patterns like StringNullVersioned, e.g. StringIntegerMinLength1.
  • I update ocdskit schema-report to check, and there are no good candidates.

Also, check whether to update extensions (all linked PRs refer to open-contracting/ocds-extensions#50):

• ocds_lots_extension: /definitions/LotDetails: null present since first commit
• ocds_location_extension: /definitions/Location/properties/geometry, /definitions/Location/properties/gazetteer: Make geometry and gazetteer nullable open-contracting-extensions/ocds_location_extension#19
• ocds_finance_extension: /definitions/Finance/properties/interestRate: Add null type to optional fields open-contracting-extensions/ocds_finance_extension#14
• ocds-shareholders-extension: /definitions/Organization/properties/beneficialOwnership: Add null type to optional fields open-contracting-extensions/ocds_shareholders_extension#16
• ocds_performance_failures: /definitions/PerformanceFailure/properties/period: Add null type to optional fields open-contracting-extensions/ocds_performance_failures_extension#10
• ocds_metrics_extension:
  • /definitions/Observation/properties/unit: null present since first commit
  • /definitions/Observation/properties/dimensions: Make nullable open-contracting-extensions/ocds_metrics_extension#17
• ocds_tariffs_extension:
  • /definitions/Observation/properties/unit: null present since first commit
  • /definitions/Observation/properties/dimensions: make dimensions nullable open-contracting-extensions/ocds_tariffs_extension#22

@kindly: If we figure that optional fields should be nullable (even if their type includes object), then we can leave the extensions as-is, I think. Do you agree?

[jpmckinney]

After doing more work on OCDS Merge and merging rules, I came to the conclusion that array and object fields should not be nullable (except in exceptional circumstances like GeoJSON fields), as this makes the merging logic even more complicated and non-obvious than it already is.