fix: s3zip in fs mode (#13758)
fix: s3zip in fs mode (#13758)

The index was converted directly from bytes to binary. This would fail a roundtrip through json.

This would result in `Error: invalid input: magic number mismatch` when reading back.

On non-erasure backends store index as base64.
vadmeste/minio,balamurugana/minio,krisis/minio,minio/minio,krisis/minio,balamurugana/minio,donatello/minio,donatello/minio,minio/minio,vadmeste/minio