[OPIK-5241] [BE] infra: auto-sync llm-models-default.yaml to CDN on model update

[obezpalko]

Details

Adds two automated behaviors to the daily provider model sync workflow:

1. YAML regeneration — sync_provider_models.py now also regenerates llm-models-default.yaml (the runtime registry consumed by LlmModelRegistryService) alongside the existing Java enum and TypeScript files. This ensures the CDN-hosted YAML stays in sync with every model update. Reasoning flags are carried over from the existing file; all other properties (structuredOutput, qualifiedName for VertexAI) are derived from the same sources as the Java enums.
2. CDN upload — after a successful sync, the updated YAML is uploaded to s3://cdn.comet.ml/opik/llm-models-default.yaml and the CloudFront distribution is invalidated so consumers pick up the new file within the configured TTL.

Change checklist

• User facing
• Documentation update

Issues

• Resolves #
• OPIK-5241

AI-WATERMARK

AI-WATERMARK: yes

• If yes:
  • Tools: Claude Code
  • Model(s): claude-sonnet-4-6
  • Scope: New regenerate_llm_models_yaml() function in sync script + workflow S3/CloudFront steps
  • Human verification: Review YAML output format matches llm-models-default.yaml schema; verify AWS credential/role/bucket/distribution variable names match infra setup

Testing

• python scripts/sync_provider_models.py --dry-run — passes, no errors
• python -c "from scripts/sync_provider_models import regenerate_llm_models_yaml ..." — verified correct YAML output: structuredOutput, reasoning, and VertexAI qualifiedName fields all render correctly; empty provider sections emit [] (valid YAML, avoids null deserialization in Jackson)
• AWS steps not run locally — depends on infra secrets/vars available only in CI

Documentation

N/A