Only done when versioning=yes is configured. It could always do it when
S3 sends back a version id, but there may be buckets that have
versioning enabled by accident, so it seemed better to honor the
configuration.
S3's docs say version IDs are "randomly generated", so presumably
storing the same content twice gets two different ones not the same one.
So I considered storing a list of version IDs for a key. That would
allow removing the key completely. But.. The way Logs.RemoteState works,
when there are multiple writers, the last writer wins. So storing a list
would need a different log format that merges, which seemed overkill to support
removing a key from an append-only remote.
Note that Logs.RemoteState for S3 is now dedicated to version IDs.
If something else needs to be stored, a new log will be needed to do it.
This commit was supported by the NSF-funded DataLad project.
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