fix(replication): avoid persisting aws-chunked metadata

[chodorenko]

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Description

Avoid persisting the SigV4 streaming transport header Content-Encoding: aws-chunked as replica object metadata.

The trusted-replication path restored all supported headers after the ordinary metadata parser had normalized them. That reintroduced the raw transport encoding, although the source object has no content encoding.

This change restores only replication-only headers after trust validation and leaves normalized ordinary metadata intact.

Motivation and Context

Replicated objects can advertise Content-Encoding: aws-chunked even though their bytes were never content-encoded. S3 clients consuming GET/HEAD responses from the replica may try to decode those bytes incorrectly.

How to test this PR?

go test ./cmd -run 'Test(ExtractMetadataHeaders|ExtractReplicationMetadataHeaders|GetCopyObjectMetadataFromHeaderReplication)' -count=1
go build -o /private/tmp/silo-aws-chunked-fix .

The updated regression test supplies trusted replication headers plus Content-Encoding: aws-chunked, and verifies that the stored metadata has no content-encoding while replication-only fields are preserved.

Compatibility impact

No API or configuration changes. Newly replicated objects no longer retain the invalid transport encoding in metadata. Existing objects with this metadata are not modified.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Optimization (provides speedup with no functional changes)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• All commits are signed off (git commit -s) per the DCO
• Fixes a regression: 56fa63b
• Unit tests added/updated
• make verifiers passes
• Relevant package tests and go build pass
• Compatibility and rollback impact documented
• Internal documentation updated
• Public documentation update opened in pgsty/silo.pgsty.com, if needed

fix for #185