[stable32] Encode s3 metadata as base64 if needed

[backportbot]

Backport of #56515

Second commit was removed, as it was a revert of a commit that had not been backported yet to stable32.

[danxuliu]

I have force pushed to remove the second commit, as it was a revert for a change that had not been merged yet in stable32. The first commit was untouched, as it was already the same as in the original pull request.

Please note that I have not been able to reproduce the original issue (using minio), so although it is likely that no other changes are needed I could not verify it (maybe something else changed in master that was not backported to stable32 🤷).