Add Apache Polaris converter module

[jbonofre]

Summary

• Adds a two-way converter between OSI semantic models and Apache Polaris catalogs under converters/polaris/
• Import mode: reads Polaris namespaces/tables via the Iceberg REST Catalog API and generates OSI YAML, mapping Iceberg schemas to OSI datasets, fields, primary keys, and temporal dimensions
• Export mode: reads OSI YAML and creates Polaris namespaces and Iceberg tables with type inference from field names and dimension metadata

Test plan

• Unit tests pass (9 tests covering parsing, YAML generation round-trip, Iceberg schema generation, type inference, and edge cases)
• Integration test against a running Polaris instance (import and export)
• Verify round-trip fidelity: Polaris → OSI → Polaris

[jbonofre]

This is a use example:

  # Import: Polaris catalog → OSI YAML
  java -jar osi-polaris-converter.jar import \
    --url http://localhost:8181 --catalog my_catalog \                                                                                                                                                                                        
    --client-id <id> --client-secret <secret> \
    -o output.yaml                                                                                                                                                                                                                            
                                                            
  # Export: OSI YAML → Polaris catalog                                                                                                                                                                                                        
  java -jar osi-polaris-converter.jar export \              
    --url http://localhost:8181 --catalog my_catalog \
    --token <bearer-token> \                                                                                                                                                                                                                  
    model.yaml

I implemented with the following logic:

• Each Polaris namespace maps to an OSI semantic model
• Each Iceberg table maps to an OSI dataset
• Iceberg schema fields map to OSI fields with ANSI_SQL expressions
• Iceberg identifier-field-ids map to OSI primary_key
• Temporal Iceberg types (timestamp, timestamptz, date) set dimension.is_time: true
• Table properties are preserved in custom_extensions

[flyrain]

Thanks for adding this, @jbonofre. Can we put it a common module instead of Polaris module? I think the Java representation would be really useful for other catalogs as well.

[jbonofre]

@flyrain That's a good idea. I think it also related to a discussion we had before: what should be the "language layout" as we have converter in Python, Java, ...

Let me give a proposal.

[flyrain]

Awesome! Looking forward to it

[jbonofre]

I'm working on a PR to have core-spec module, that will create bindings for different languages (including java).

[jbonofre]

@khush-bhatia I'm preparing a first step PR with core-spec and java binding.

[sgandon]

LGTM

[jbonofre]

I created #121 for follow up.