[FLINK-39499][tests] Launch the SeaweedFS S3 test backend via 'weed mini'

[chrislusf]

What is the purpose of the change

Simplify the SeaweedFS-backed S3 test setup. The container is now launched with weed mini, which pre-creates the bucket (-bucket) and reports readiness only after every component is up. Both the Java test container and the S3 end-to-end script rely on that instead of creating the bucket client-side.

Brief change log

• SeaweedFsTestContainer: run mini -bucket=<bucket>; wait on mini's readiness log message; drop the client-side createDefaultBucket() and the withStartupAttempts(3) startup-503 workaround.
• common_s3_seaweedfs.sh: run mini -bucket=$IT_CASE_S3_BUCKET; wait on the readiness log message instead of /healthz; drop the explicit aws s3 mb.

Verifying this change

This change is already covered by existing tests: the SeaweedFS S3 ITCases (e.g. HAJobRunOnHadoopS3FileSystemITCase, S5CmdOnSeaweedFsITCase) and the S3 end-to-end tests, which exercise the modified container and script setup.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no (test infrastructure only)

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not applicable

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Was generative AI tooling used to co-author this PR?

• Yes (Claude Code, claude-opus-4-8)

Generated-by: Claude Code (claude-opus-4-8)

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CI report:

• 2dd4b41 Azure: SUCCESS

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