Preserve catalog storage names in setup round trips

[mattfaltyn]

Summary

polaris setup export omitted a catalog's optional storageName, and the apply
path could not restore it. A successful backup, migration, or bootstrap round
trip therefore changed credential selection when
RESOLVE_CREDENTIALS_BY_STORAGE_NAME was enabled.

This change preserves the field across export and apply for every supported
storage type. Existing setup files remain compatible because storage_name is
optional and defaults to None when absent.

Fixes #5344.

Changes

• Export storageName as storage_name in setup YAML.
• Map the optional field through setup apply and all catalog storage model
  builders.
• Extend the S3 setup round-trip regression test to assert the exported and
  recreated storage name.
• Document the optional setup field and add an unreleased changelog entry.

Validation

• JAVA_HOME=/private/tmp/polaris-jdk21/Contents/Home ./gradlew format compileAll
  — passed (981 actionable tasks).
• JAVA_HOME=/private/tmp/polaris-jdk21/Contents/Home make client-regenerate
  — passed.
• JAVA_HOME=/private/tmp/polaris-jdk21/Contents/Home make client-unit-test
  — passed (193 tests).
• make client-lint — passed (trailing whitespace, EOF, debug statements,
  Ruff check/format, MyPy).
• make client-license-check — passed.
• YAML parse of reference-setup-config.yaml and git diff --check — passed.

Checklist

• 🛡️ This is a non-security configuration-fidelity bug; no security issue is disclosed.
• 🔗 The need and current failure mode are documented in Fixes Python CLI setup round trip drops catalog storageName #5344.
• 🧪 The setup export/apply regression test covers the lossy round trip.
• 💡 No complex logic was added that requires explanatory comments.
• 🧾 Updated CHANGELOG.md under Unreleased / Fixes.
• 📚 Updated the setup reference configuration; the existing unreleased CLI guide already links it and its setup contract is unchanged.

AI assistance

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