test(opensearch): pin OpenSearchRunner HTTP port to avoid flaky tests

[marevol]

Summary

The OpenSearch backend tests intermittently fail to start the embedded node with "Address already in use". OpenSearchRunner selects its HTTP port via a connect-based scan that can report a port as free even when it is already bound on the IPv6 loopback ([::1]), so the node occasionally tries to bind a port that is not actually available. This PR makes the test setup deterministic by reserving a free ephemeral port up front and pinning the runner to it.

Changes Made

• Added OpenSearchRunnerUtil test helper with findFreePort(), which asks the OS for an ephemeral port via new ServerSocket(0).
• Updated CrawlerTest, OpenSearchDataServiceTest, OpenSearchUrlFilterServiceTest, and OpenSearchUrlQueueServiceTest to:
  • Reserve a free port before building the runner.
  • Disable the unreliable port scan via runner.setMaxHttpPort(-1).
  • Pass baseHttpPort(httpPort - 1) so the first node binds to the reserved port (the runner uses baseHttpPort + 1 for the first node).
  • Use the reserved port as the fallback value for the FesenClient.HTTP_ADDRESS system property.

Testing

• Test-only change. Run the OpenSearch module tests (mvn test -pl fess-crawler-opensearch) to confirm the embedded node starts reliably.

Breaking Changes

• None. Changes are limited to test code.

Additional Notes

• The same setup pattern is duplicated across the four test classes for consistency; the shared logic lives in OpenSearchRunnerUtil.