Add upgrade compatibility restore workflow

SeaTunnel had strong normal CI coverage, but no recurring lane proving that persisted runtime state from a previous stable release can be restored by current dev across representative stateful jobs.

Added a GitHub Actions workflow and scenario-driven runner that builds current dev, downloads the previous release, creates savepoints with the older release, restores with current dev, and verifies restored output through Assert scenarios.

• Creates an automated early-warning lane for stateful upgrade regressions that normal fresh-start CI can miss.
• Covers both service-free FakeSource to LocalFile restore and MySQL CDC multi-table restore scenarios.
• Provides a reusable scenario structure so future CDC or connector-specific restore cases can be added without rewriting the workflow.

• Added shell, YAML, scenario, README, setup, teardown, and assert artifacts for the compatibility runner.
• Stabilized the generic restore case after review by keeping it on a live long-running path before savepoint.
• Maintainer approval recognized the workflow as a useful starting point for SeaTunnel upgrade validation.