s3: fix PutObject ETag format for multi-chunk uploads (#7771)

* s3: fix PutObject ETag format for multi-chunk uploads

Fix issue #7768: AWS S3 SDK for Java fails with 'Invalid base 16
character: -' when performing PutObject on files that are internally
auto-chunked.

The issue was that SeaweedFS returned a composite ETag format
(<md5hash>-<count>) for regular PutObject when the file was split
into multiple chunks due to auto-chunking. However, per AWS S3 spec,
the composite ETag format should only be used for multipart uploads
(CreateMultipartUpload/UploadPart/CompleteMultipartUpload API).

Regular PutObject should always return a pure MD5 hash as the ETag,
regardless of how the file is stored internally.

The fix ensures the MD5 hash is always stored in entry.Attributes.Md5
for regular PutObject operations, so filer.ETag() returns the pure
MD5 hash instead of falling back to ETagChunks() composite format.

* test: add comprehensive ETag format tests for issue #7768

Add integration tests to ensure PutObject ETag format compatibility:

Go tests (test/s3/etag/):
- TestPutObjectETagFormat_SmallFile: 1KB single chunk
- TestPutObjectETagFormat_LargeFile: 10MB auto-chunked (critical for #7768)
- TestPutObjectETagFormat_ExtraLargeFile: 25MB multi-chunk
- TestMultipartUploadETagFormat: verify composite ETag for multipart
- TestPutObjectETagConsistency: ETag consistency across PUT/HEAD/GET
- TestETagHexValidation: simulate AWS SDK v2 hex decoding
- TestMultipleLargeFileUploads: stress test multiple large uploads

Java tests (other/java/s3copier/):
- Update pom.xml to include AWS SDK v2 (2.20.127)
- Add ETagValidationTest.java with comprehensive SDK v2 tests
- Add README.md documenting SDK versions and test coverage

Documentation:
- Add test/s3/SDK_COMPATIBILITY.md documenting validated SDK versions
- Add test/s3/etag/README.md explaining test coverage

These tests ensure large file PutObject (>8MB) returns pure MD5 ETags
(not composite format), which is required for AWS SDK v2 compatibility.

* fix: lower Java version requirement to 11 for CI compatibility

* address CodeRabbit review comments

- s3_etag_test.go: Handle rand.Read error, fix multipart part-count logging
- Makefile: Add 'all' target, pass S3_ENDPOINT to test commands
- SDK_COMPATIBILITY.md: Add language tag to fenced code block
- ETagValidationTest.java: Add pagination to cleanup logic
- README.md: Clarify Go SDK tests are in separate location

* ci: add s3copier ETag validation tests to Java integration tests

- Enable S3 API (-s3 -s3.port=8333) in SeaweedFS test server
- Add S3 API readiness check to wait loop
- Add step to run ETagValidationTest from s3copier

This ensures the fix for issue #7768 is continuously tested
against AWS SDK v2 for Java in CI.

* ci: add S3 config with credentials for s3copier tests

- Add -s3.config pointing to docker/compose/s3.json
- Add -s3.allowDeleteBucketNotEmpty for test cleanup
- Set S3_ACCESS_KEY and S3_SECRET_KEY env vars for tests

* ci: pass S3 config as Maven system properties

Pass S3_ENDPOINT, S3_ACCESS_KEY, S3_SECRET_KEY via -D flags
so they're available via System.getProperty() in Java tests

weed/s3api/s3api_object_handlers_put.go

@@ -506,20 +506,14 @@ func (s3a *S3ApiServer) putToFiler(r *http.Request, filePath string, dataReader
 		Extended: make(map[string][]byte),
 	}
 
-	// Set Md5 attribute based on context:
-	// 1. For multipart upload PARTS (stored in .uploads/ directory): ALWAYS set Md5
-	//    - Parts must use simple MD5 ETags, never composite format
-	//    - Even if a part has multiple chunks internally, its ETag is MD5 of entire part
-	// 2. For regular object uploads: only set Md5 for single-chunk uploads
-	//    - Multi-chunk regular objects use composite "md5-count" format
-	isMultipartPart := strings.Contains(filePath, "/"+s3_constants.MultipartUploadsFolder+"/")
-	if isMultipartPart || len(chunkResult.FileChunks) == 1 {
-		entry.Attributes.Md5 = md5Sum
-	}
+	// Always set Md5 attribute for regular object uploads (PutObject)
+	// This ensures the ETag is a pure MD5 hash, which AWS S3 SDKs expect
+	// for PutObject responses. The composite "md5-count" format is only
+	// used for multipart upload completion (CompleteMultipartUpload API),
+	// not for regular PutObject even if the file is internally auto-chunked.
+	entry.Attributes.Md5 = md5Sum
 
-	// Calculate ETag using the same logic as GET to ensure consistency
-	// For single chunk: uses entry.Attributes.Md5
-	// For multiple chunks: uses filer.ETagChunks() which returns "<hash>-<count>"
+	// Calculate ETag - with Md5 set, this returns the pure MD5 hash
 	etag = filer.ETag(entry)
 	glog.V(4).Infof("putToFiler: Calculated ETag=%s for %d chunks", etag, len(chunkResult.FileChunks))