Right now backup to S3 does not make a lot of sense, since:
- it has random names, and to decoding them
- requires metadata from local disk (/var/lib/disks/DISK/BACKUP_NAME)
- or send_metadata (but it is also tricky even with it)
So this patch adds simpler interface for S3, it is only suitable for
BACKUP/RESTORE, so don't try to use it for MergeTree engine.
It is done by adding separate disk - `s3_plain` for this, that:
- does not support any extended features, like renames/hardlinks/attrs/...
(so basically everything that MergeTree requires)
- only write/read/unlink/list files
Signed-off-by: Azat Khuzhin <a.khuzhin@semrush.com>
