docs: Polaris integration guide for Table Topic with REST custom headers

[aaron-seq]

Move Polaris integration docs from core repo PR to labs with runnable setup:

• Add table-topic-solutions/polaris-integration with README, docker-compose, configs, and scripts
• Document header pattern:
  • automq.table.topic.catalog.header.Authorization
  • automq.table.topic.catalog.header.Polaris-Realm
• Provide end-to-end compose stack (MinIO, Polaris, AutoMQ, Spark)
• Include troubleshooting and quick validation steps

This addresses maintainer guidance to host integration examples in labs, keeping core repo docs minimal.

[daniel-y]

@aaron-seq Cool, thanks for your contribution, let us have a check and merge it!

[Gezi-lzq]

Based on reviewing the integration approach in this PR, I believe the provided docker-compose configuration cannot actually offer the service. To ensure efficient reviews and build trust in the PR, please ensure that code changes are fully tested locally before submitting.