[FLINK-39530][s3] Replace S3 compatible auto-detection with explicit chunked-encoding and checksum-validation config options

[gaborgsomogyi]

What is the purpose of the change

This is a backport of #28009.

The native S3 connector previously treated any custom s3.endpoint as an indicator of an S3-compatible server, silently enabling path-style access and disabling chunked encoding and checksum validation. This caused legitimate AWS regional endpoints (e.g. s3.us-west-2.amazonaws.com) to be misconfigured with no workaround available.

This PR removes the auto-detection entirely and introduces two explicit config options:

• s3.chunked-encoding.enabled (default: true)
• s3.checksum-validation.enabled (default: true)

The existing s3.path-style-access option already served as an explicit knob. Users targeting S3-compatible servers (MinIO, Ceph, etc.) now configure all three flags explicitly.

Additionally, S3ClientProvider now stores and exposes all directly configurable flags (pathStyleAccess, chunkedEncoding, checksumValidation, maxConnections, maxRetries) for testability, and the test suite was refactored to assert actual config values rather than fs != null.

Brief change log

• Removed auto server detection
• Added s3.chunked-encoding.enabled (default: true)
• Added s3.checksum-validation.enabled (default: true)
• Tests simplifition
• Additional tests for coverage

Verifying this change

Existing and newly added tests.

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: yes

Documentation

• Does this pull request introduce a new feature? nono
• If yes, how is the feature documented? not applicable

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

• Yes

Generated-by: Claude Code

[gaborgsomogyi]

cc @mbalassi @ferenc-csaky

[flinkbot]

CI report:

• 3b2083c Azure: SUCCESS

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot run azure re-run the last Azure build

[Samrat002]

Considering CI is green