Extend json-schema model parser

Summary

For https://gitlab.indiscale.com/caosdb/customers/3dmmto/management/-/issues/9.

This implements

• pattern properties
• type null properties
• json schema references
• and json schemas without top-level recordtype specification

for the json schema datamodel parser.

Focus

Mainly additions to the JsonSchemaParser class. We also defined a treatment for type: array properties that lack a strict items specification (i.e., could be lists of elements with mixed types, so a manual specification has to be provided -- or they are ignored altogether).

Test Environment

New unit tests. You can also test it with the chemotion json schema in nextcloud/Customers/3dmmto/example_files/testdaten_chemotion/schema.json.

Check List for the Author

Please, prepare your MR for a review. Be sure to write a summary and a focus and create gitlab comments for the reviewer. They should guide the reviewer through the changes, explain your changes and also point out open questions. For further good practices have a look at our review guidelines

• All automated tests pass
• Reference related issues
• Up-to-date CHANGELOG.md (or not necessary)
• Up-to-date JSON schema (or not necessary)
• Appropriate user and developer documentation (or not necessary)
  • How do I use the software? Assume "stupid" users.
  • How do I develop or debug the software? Assume novice developers.
• Annotations in code (Gitlab comments)
  • Intent of new code
  • Problems with old code
  • Why this implementation?

Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md (or not necessary)
• Appropriate user and developer documentation (or not necessary)
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.
• Check: Are there specifications? Are they satisfied?

For further good practices have a look at our review guidelines.

unittests/json-schema-models/datamodel_missing_array_items.schema.json

+{
+    "title": "something_with_missing_array_items",
+    "type": "object",
+    "properties": {
+        "missing": {
+            "type": "array"
+        }
+    }
+}