before this change, we enumerate the sstables tracked by the
system.sstables table, and restore them when serving
requests to "storage_service/restore" API. this works fine with
"storage_service/backup" API. but this "restore" API cannot be
used as a drop-in replacement of the rclone based API currently
used by scylla-manager.
in order to fill the gap, in this change:
* add the "prefix" parameter for specifying the shared prefix of
sstables
* add the "sstables" parameter for specifying the list of TOC
components of sstables
* remove the "snapshot" parameter, as we don't encode the prefix
on scylla's end anymore.
* make the "table" parameter mandatory.
Fixesscylladb/scylladb#20461
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>