[FLINK-34324][test] Makes all s3 related operations being declared and called in a single location

[XComp]

What is the purpose of the change

This PR contains some refactorings of the s3-related tests. I moved the branch from my fork (see related PR #24244) to the main repo to check whether this would enable the s3 related tests without merging the PR to master.

Brief change log

• Fixes error message in test execution
• unifies S3-related code in one location

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

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

Documentation

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

[flinkbot]

CI report:

• 2d78f0d Azure: PENDING

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[XComp]

I deleted the branch again because it doesn't enable the S3 credentials, of course. 🤦 Anyway, it's better to replace it with Minio.