[FLINK-39709][s3]Update documentation for native-s3 Implementation

[Samrat002]

What is the purpose of the change

Update missing configuration for native-s3-fs.

Brief change log

Update ReadMe doc

Verifying this change

N/A

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

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: (yes / no / don't know)
• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no / don't know)

Documentation

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

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CI report:

• b4c4948 Azure: SUCCESS

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[gaborgsomogyi]

Issue 1 — MinIO section: auto-detection claim is incorrect (~line 263)

Current text:

MinIO-specific optimizations are applied automatically:
- Path-style access enabled
- Chunked encoding disabled (compatibility)
- Checksum validation disabled (compatibility)

s3.chunked-encoding.enabled and s3.checksum-validation.enabled are plain ConfigOptions with defaultValue(true) (NativeS3FileSystemFactory.java:101–115). There is no code that auto-disables them when a custom endpoint is set — only path-style access is auto-enabled (S3ClientProvider.java:481). A user copying the MinIO example as-is will have both still on, which can cause request failures against MinIO.

Suggested replacement:

When a custom endpoint is configured, path-style access is enabled automatically.
Chunked encoding and checksum validation must be disabled manually for MinIO compatibility:

```yaml
s3.chunked-encoding.enabled: false
s3.checksum-validation.enabled: false

[gaborgsomogyi]

Issue 2 — SSE type table: aliases not documented (~line 80)

Current text:

| s3.sse.type | none | Encryption type: `none`, `sse-s3` (AES256), `sse-kms` (AWS KMS) |

S3EncryptionConfig.java:143–147 has explicit case "aes256" and case "aws:kms" branches. The aws:kms value in particular is what Hadoop S3A configs use, so users migrating from Hadoop will set it and silently get no encryption (falls through to none) because it is undocumented.

Suggested replacement:

| s3.sse.type | none | Encryption type: `none`, `sse-s3` or `aes256` (S3-managed keys), `sse-kms` or `aws:kms` (KMS-managed keys) |